IPCS INCHEM Home

    ETHEPHON

    First draft prepared by
    J-J. Larsen
    National Food Agency of Denmark, Soborg, Denmark

    EXPLANATION

         Ethephon was evaluated at the 1978 JMPR, but an ADI was not
    allocated since the available toxicological data were insufficient
    (Annex 1, reference 30). It is a plant growth regulator that acts by
    release of ethylene, influencing directly several physiological
    processes such as ripening and maturation and stimulating the
    production of endogenous ethylene. Since the compound in high
    concentration (> 87%) is a waxy solid and difficult to handle, a
    technical product that contains 71% ethephon and 21% water is
    marketed and also used for most toxicological studies. Although
    ethephon is a dibasic phosphonic acid, its commercial formulation
    exhibits some anticholinesterase activity.

    EVALUATION FOR ACCEPTABLE DAILY INTAKE

    BIOLOGICAL DATA

    Biochemical aspects

    Absorption, distribution, and excretion

    Rats

         The absorption, distribution, metabolism, and elimination of
    14C-ethephon was studied by single and multiple dose regimens in
    male and female Crl:CD(SD)BR rats. Unlabelled ethephon (purity
    96.1%) and 14C-ethephon (radiochemical purity > 96%,) dissolved
    in methanol, soluted with a 0.9% (w/v) sodium chloride, and adjusted
    to a pH of 3-4 with lactic acid were used. The compound was
    administered orally to 5 male and 5 female rats in a single dose of
    50 or 1000 mg/kg bw (dose volume 5 ml/kg bw, radioactivity 10
    µCi/g), multiple oral doses of 50 mg/kg bw (non-radiolabelled
    ethephon administered daily for 14 days followed 24 hours later by a
    single dose of 14C-ethephon), or intravenously to 5 male and 5
    female rats in a dose of 50 mg/kg bw (dose volume 1 ml/kg bw,
    radioactivity 60 µCi/g). Urine and faeces were collected in
    individual all-glass metabolism cages for 7 days. Expired
    radioactivity was captured by a mercuric perchlorate and 2-ethoxy
    ethanol: ethanolamine-containing trapping system. Urine, faeces, and
    volatile trap solutions were collected at intervals up to 120 hours
    after dosing, after which the rats were sacrificed and tissues taken
    at necropsy for radioactivity measurement. In a parallel
    pharmacokinetic study using a single dose of 50 or 1000 mg/kg bw,
    blood was sampled from the lateral tail vein at intervals up to 168
    hours and the concentration of radioactivity in whole blood was
    determined.

         Blood levels of radioactivity (50 or 1000 mg/kg bw) peaked at
    0.5-2 hours post-dose and declined exponentially with levels near
    background by 12-24 hours post-dose. Following a single oral dose of
    14C-ethephon (50 mg/kg bw), about 90% of the administered
    radioactivity was recovered, principally in urine (55%), expired air
    (20%), and faeces (5%) during 120 hours after dosing. Most of the
    dose was recovered within 24 hours post-dose. Pretreatment with non-
    radiolabelled ethephon did not significantly alter tissue residues
    at 120 hours post-dose over those animals receiving a single
    administration only. Following a single oral dose of 14C-ethephon
    (1000 mg/kg bw) about 86% of the administered radioactivity was
    recovered, principally in urine (48%), expired air (19%), and faeces
    (6%) at 120 hours post-dose. Most of the dose was recovered within
    24 hours post-dose. No major sex difference in pharmacokinetics was
    observed (Savage, 1990).

    Dogs

         The disposition of ethephon was studied in 3 male beagle dogs.
    The animals, weighing 6.1-6.3 kg, were placed for 72 hours
    acclimatization in individual metabolism cages the week before
    dosing. A single oral dose of 180 mg/kg bw made up of 1.5 ml of a
    methanolic 14C-ethephon solution (362.6 µCi/5 ml) and 2.0 ml of a
    5 normal citric acid non-radiolabelled ethephon solution (purity
    88%) was given in a 4 ml gelatin capsule. Ethylene and carbon
    dioxide were collected from the expired air by a carbon dioxide and
    ethylene-trapping system, and blood samples, urine, and faeces were
    collected at intervals for scintillation counting. Blood samples
    were also used for determination of RBC and plasma cholinesterase
    levels. The animals were sacrificed 72 hours after dosing and
    tissues removed for scintillation counting. Two of the three dogs
    vomited 15-30 min after dosing thus questioning the dosing.

         About 35% of the dose appeared in the urine of two dogs within
    24 hours after dosing. The radioactivity in urine dropped within 72
    hours to levels below 1%. In one dog receiving the full dosage, 4,
    0.1, and 0.03% of the dose was found in faeces at 24, 48, and 72
    hours after dosing, respectively. In this dog, 30% of the dose was
    recovered as ethylene in the expired air and only traces of
    14CO2 were recovered. Total selected organs retained at
    sacrifice a maximum of 0.25% of the administered dose. Peak plasma
    and blood cell concentrations were observed 2 hours after dosing.
    Only traces were observed after 22 hours. Plasma cholinesterase
    levels were reduced at 2 hours with recovery starting within a few
    hours. Erythrocyte cholinesterase levels responded more slowly with
    signs of recovery at 72 hours (Stephen & Walker, 1971).

    Biotransformation

    Rats

         The mono- and di-sodium salts of ethephon, and some
    unidentified metabolites were present in urine and faeces of male
    and female Crl:CD(SD)BR rats dosed with single (50 or 1000 mg/kg bw)
    or multiple dosages (50 mg/kg bw) of 14C-ethephon (Savage, 1990).
    Ethylene was eliminated in the expired air. No significant sex,
    route or dose differences in metabolism were observed (Hardy  et
     al., 1990).

    Dogs

         The urine of 3 beagle dogs was examined by thin layer and gas
    chromatography following a single oral dose of 180 mg/kg bw 14C-
    ethephon made up of 1.5 ml of a methanolic 14C-ethephon solution
    (362.6 µCi/5 ml) and 2.0 ml of a 5 normal citric acid non-
    radiolabelled ethephon solution (purity 88%) (Stephen & Walker,

    1971). Ethephon was partly excreted unchanged in the urine and also
    metabolized to ethylene and eliminated in the expired air (Stephen &
    Stanovick 1971).

    Effects on enzymes and other biochemical parameters

         In beagle dogs dosed with 180 mg/kg bw ethephon, plasma
    cholinesterase activity was inhibited at 2 hours with recovery
    starting within a few hours. Erythrocyte cholinesterase levels
    responded more slowly with signs of recovery at 72 hours. Very
    sparse information on the test procedures, including time schedule
    for sampling and measurements, was available (Stephen & Walker,
    1971).

    Toxicological studies

    Acute toxicity studies

         Ethephon has a low oral acute toxicity in mice, rats, and
    rabbits. The LD50 or LC50 values are given in Table 1. WHO has
    classified ethephon as unlikely to represent acute hazard in normal
    use (WHO, 1992).

        Table 1. Acute toxicity of ethephon
                                                                                             
    Species   Sex    Route        Purity       LD50       LC50       Reference
                                    (%)     (mg/kg bw)   (mg/m3)
                                                                                             

    Mouse     M      oral           90         1920                  Holsing, 1969

    Rat       M      oral           71         3730                  Myers, 1984

    Rat       M      oral           71         2210                  Myers, 1984

    Rat       F      inh. (4 h)     72                    4500       Nachreiner & Klonne, 1989

    Rat       F      inh. (4h)      72                    4500       Nachreiner & Klonne, 1989

    Rabbit    F      oral           90         > 560                 Weatherholtz, 1989

    Rabbit    M      dermal         71         1700                  Meyers, 1989

    Rabbit    F      dermal         71         1400                  Meyers, 1989

                                                                                             
    
    Short-term toxicity studies

    Mice

         A 4-week dietary study in mice was carried out with ethephon.
    After 2 weeks' acclimatization, groups of 10 CD-1 mice/sex received
    in the diet 0, 30, 100, 300, 1000, or 3000 ppm ethephon (purity
    71%), equal to 0, 5.3, 18, 51, 181, or 546 mg/kg bw/day in males and
    0, 6.5, 22, 69, 210, or 635 mg/kg bw/day in females. An additional 5
    animals/sex were included in the 0, 300, and 1000 ppm groups for 2-
    week cholinesterase activity determinations. The mice were 7 weeks
    of age at initiation of dosing. Stability and homogeneity of the
    test substance in the diet was not examined. No effects were
    observed in the incidence of clinical signs or mortality, food
    consumption, body weight, organ weights or ASAT, SDH, ALP, ALT or
    brain ChE activity at any dose level. Biologically significant (>
    20%) inhibition of plasma ChE activity was observed at 300 ppm (18-
    22% in males and 23-29% in females), 1000 ppm (43-44% in males and
    46-49% in females) and 3000 ppm (63% in males and 55% in females).
    Significant inhibition of RBC was observed at 1000 ppm (29-34% in
    males and 38-41% in females) and 3000 ppm (62% in males and 56% in
    females). A statistically significant decrease (26%) in SDH was seen
    in the female high-dose group, and a statistically significant
    increase (24%) was seen in ALP in males of the high-dose group.
    Based on erythrocyte cholinesterase inhibition, the NOAEL was 300
    ppm equal to 51 and 69 mg/kg bw/day in male and female mice,
    respectively (Miller & Troup, 1986a).

         In order to establish an MTD for ethephon in mice, a 4-week
    dietary study was carried out. After 2 weeks' acclimatization,
    groups of 15 CD-1 mice/sex received in the diet 0, 3000, 10 000,
    25 000, or 50 000 ppm ethephon (purity 71%), equal to 0, 530, 1800,
    4500, or 10 000 mg/kg bw/day in males and 0, 630, 2200, 5900, or
    15 000 mg/kg bw/day in females. No effects were observed in the
    incidence of clinical signs or mortality. Food consumption reduction
    in the 50 000 ppm group at week 1 and body-weight reductions in the
    same group throughout the study for both sexes were; attributed
    primarily to initial aversion to the test diets. For male mice,
    organ weight changes at 28 days were consistent with the decreased
    body weights. In females, a larger than expected reduction in spleen
    weight, which was reflected in a decreased spleen to final body
    weight and spleen to brain weight ratios, was observed in the 50 000
    ppm group. The significance of this finding could not be determined.
    Dose-related inhibition of plasma (54-82%) and erythrocyte (54-92%)
    ChE activity was observed in both sexes at 2 and 4 weeks. Brain ChE
    activity was not inhibited. Based on the finding that only plasma
    and erythrocyte ChE activities were inhibited and only minimal
    additional biological responses were observed, an initial high dose
    of 50 000 ppm was established for oncogenicity testing of ethephon
    in mice (Miller & Troup, 1986b).

    Rats

         A 4-week dietary toxicity study was carried out with ethephon
    in rats. After 2 weeks' acclimatization, groups of 10 Sprague-Dawley
    CD rats/sex received in the diet 0, 625, 1250, 2500, 5000, or 10 000
    ppm ethephon (purity 71%), equal to 0, 52, 106, 214, 430, or 830
    mg/kg bw/day in males and 0, 59, 120, 251, 487, or 980 mg/kg bw/day
    in females. An additional 5 animals/sex were included in the 0,
    1250, and 2500 ppm groups for 2-week cholinesterase activity
    determinations.

         No clinical signs of toxicity and no statistically significant
    effect on food consumption, body weight, haematology, or clinical
    chemistry were observed in either sex at any dosage level.
    Inhibition of plasma ChE activity was 21-27% at 1250 ppm, 16-18% at
    2500 ppm, 30% at 5000 ppm and 35% at 10 000 ppm in males and 29% at
    625 ppm, 44-50% at 1250 ppm, 45-50% at 2500 ppm, 49% at 5000 ppm and
    63% at 10 000 ppm in females. The inhibition of erythrocyte ChE
    activity was 16-22% at 1250 ppm, 36-41% at 2500 ppm, 58% at 5000 ppm
    and 73% at 10 000 ppm in males and 14-35% at 1250 ppm, 32-50% at
    2500 ppm, 67% at 5000 ppm and 78% at 10 000 ppm in females. Brain
    ChE activity was not inhibited at any dose level. The NOAEL for
    ethephon in this study, based on erythrocyte ChE inhibition, was 625
    ppm, equal to 52 and 59 mg/kg bw/day in males and females,
    respectively (Miller & Troup, 1986c).

         In order to establish an MTD for ethephon in rats, a 4-week
    dietary toxicity study was carried out. After 2 weeks'
    acclimatization, groups of 15 Sprague-Dawley CD rats/sex received in
    the diet 0, 10 000, 25 000, or 50 000, ppm ethephon (purity 71%),
    equal to 0, 962, 2300, or 4673 mg/kg bw/day in males and 0, 996,
    2488, or 4900 mg/kg bw/day in females. Initial aversion to the test
    diets, resulting in decreased body weight was observed in both sexes
    in the 25 000 and 50 000 ppm groups. Inhibition of erythrocyte ChE
    activity (69-91%) and plasma ChE activity (23-74%) was cumulative
    and dose-related in both sexes. Brain ChE activity was not inhibited
    at any dose level. Diarrhoea, associated with cholinesterase
    inhibition, was observed from day 10 in the 50 000 ppm group. Based
    on the rapid development of diarrhoea in the 50 000 ppm group, an
    initial high dose of 30 000 ppm was established for chronic toxicity
    and oncogenicity testing of ethephon in rats (Miller & Troup,
    1986d).

    Rabbits

         A 21-day toxicity test was carried out with dermal application
    of ethephon in rabbits. Groups of 5-10 male and female adult New
    Zeeland white rabbits weighing 2.0-2.9 kg, received five days a
    week, for three weeks, on the abdominal skin clipped free of hair 0,
    300, or 600 mg/kg bw/day ethephon (purity 39.5%, stability and

    compound verification data not given). After 6-8 hours' exposure,
    the abdomen was washed with water. The general appearance,
    behaviour, body weight, clinical chemistry, signs of dermal
    irritation, gross pathology and histopathology were studied. No
    systemic toxicity of ethephon was demonstrated at the two dose
    levels apart from a severe dermal irritation characterized by
    subepidermal fibrosis, acanthosis, hyperkeratosis, and ulceration of
    the epidermis (Holsing, 1969).

    Dogs

         A one-year dietary toxicity study in dogs was carried out with
    ethephon. After 10 weeks' acclimatization, groups of 5 beagle
    dogs/sex received in the diet 0, 100, 300, 1000, or 2000 ppm
    ethephon (purity 71%), equal to 0, 2.8, 8.1, 27, or 54 mg/kg bw/day
    in males and 0, 2.6, 8.4, 30, or 50 mg/kg bw/day in females. Mean
    values for homogeneity and stability assays were within acceptable
    ranges.

         The methodology for diet analyses of ethephon was initially
    unsatisfactory and was changed during the study. During the first 10
    weeks of dosing, examples of great variation (e.g., 260% and 60%)
    between duplicate samples were seen. These initial problems were
    solved. After week 11, all diets analyzed were generally within 10%
    of the target levels. There was a higher incidence of soft stools in
    the ethephon-treated groups, and there was a significant decrease in
    terminal body weights, absolute and relative spleen weight (spleen-
    to-body-weight ratio, and spleen-to-brain weight ratio), absolute
    heart and thyroid/parathyroids weights for the 2000 ppm males when
    compared to control values. For the 2000 ppm females, a significant
    decrease in relative spleen weight and a significant increase in
    kidney/brain weight ratio was seen. Based on the findings of soft
    stools and changes in body weight and spleen weight, the NOAEL was
    1000 ppm, equal to 27 mg/kg bw/day in males and 30 mg/kg bw/day in
    females (Hamada, 1989).

         In a 2-year study, groups of 6 beagle dogs/sex received in the
    diet 0, 30, 300, or 1500 ppm ethephon (purity 75.6%), equal to 0,
    0.86, 7.6, or 42 mg/kg bw/day in males and 0, 0.86, 8.4, or 47.8
    mg/kg bw/day in females.

         Treatment-related findings included an increased incidence of
    soft stools in the 300 and 1500 ppm groups. Statistically
    significant erythrocyte ChE inhibition occurred in the 300 ppm group
    (42-56% in males and 36-56% in females) and in the 1500 ppm group
    (68-79% in males and 59-79% in females), and a statistically
    significant plasma ChE inhibition occurred in the 30 ppm (22-31% in
    males and 24-38% in females), 300 ppm (46-62% in males and 51-58% in
    females), and 1500 ppm (45-67% in males and 59-66% in females)
    groups. In treated groups, brain ChE values ranged from 3.7-52%

    above the control values. Compound-related gross pathology findings
    included thickened stomach and intestinal walls in dogs from all
    groups and compound-related histopathology consisted of smooth
    muscle hypertrophy in the stomach and small intestine in the 300 and
    1500 ppm groups. Based on the inhibition of erythrocyte ChE activity
    and smooth muscle hypertrophy in the stomach and small intestine,
    the NOAEL in this study was 30 ppm, equal to 0.86 mg/kg bw in both
    males and females (Reno & Voelker, 1977).

    Long-term toxicity/carcinogenicity studies

    Mice

         Male and female Swiss Albino mice (85/sex/group) were fed diets
    containing ethephon (purity 75%) at concentrations of 0, 30, 300, or
    1000 ppm for 78 weeks, equivalent to 0, 4.5, 45, or 150 mg/kg
    bw/day. Statistically significant decreases in survival were noted
    among 300 and 1000 ppm males. The increased mortality was considered
    related to genitourinary infections, dermatitis and haematopoietic
    tumours and not compound-related. Ethephon caused a dose-related
    inhibition of plasma ChE activity in both sexes (9-34% in the 300
    ppm group, and 37-64% in the 1000 ppm group). Similar results were
    observed in erythrocyte ChE activity measurements (11-56% at 300 ppm
    and 13-51% at 1000 ppm). Ethephon treatment did not cause
    biologically significant inhibition of brain ChE at any dietary
    concentration (0-9%). The incidences of haematopoietic tumours were
    4, 3, 13, and 11% in males and 22, 18, 39 and 29% in females at 0,
    30, 300, and 1000 ppm, respectively. The major contributing factor
    to the increase of 39% in the 300 ppm females was the incidence of
    thymic lymphoma involving the thymus itself (incidence of 5, 5, 19,
    and 13% at dose levels of 0, 30, 300, and 1000 ppm, respectively).
    Since the incidence of haematopoietic tumours was not significantly
    increased in females at the 1000 ppm level, the increased incidence
    in the 300 ppm females was considered as random variation and
    unrelated to ethephon administration. Based on inhibition of
    erythrocyte ChE activity, the NOAEL was 30 ppm, equivalent to 4.5
    mg/kg bw/day. There was no evidence of carcinogenicity (Voss &
    Becci, 1985).

         Male and female CD-1 mice (70/sex/group) were fed diets
    containing ethephon (purity 71.6%) at concentrations of 0, 100,
    1000, or 10 000 ppm for 78 weeks, equal to 0, 14, 140, or 1480 mg/kg
    bw/day (males) and 0, 17, 170, or 1780 mg/kg bw/day (females). An
    additional group (70 males and 70 females), that received 50 000
    ppm, were sacrificed in the first week of the study due to extensive
    morbidity and mortality after several days of dosing. An interim
    sacrifice (20 mice/sex per group) was performed at 52 weeks of
    treatment. Data on homogeneity and stability were acceptable.
    Concentration verifications of the diets gave analytical values
    ranging from 88-111% of nominal concentrations. No treatment-related

    changes were observed in the incidence of abnormal clinical signs,
    mortality, food consumption, efficiency of food utilization, water
    consumption, or incidence of ophthalmic findings during the study.
    Body weight and weight gain for males were not affected throughout
    the study. No altered haematology measurements, serum chemistry
    measurements (except ChE inhibition), organ weights, gross
    pathological observations, or histopathological observations were
    related to ethephon exposure at the 52-week or 78-week evaluation
    periods. Potentially treatment-related findings included depressed
    body weights and weight gains in females from the 10 000 ppm dose
    group that were evident starting at approximately 39 weeks. In
    addition, decreased urine pH, presumably resulting from the highly
    acidic nature of the test material, was observed in male mice from
    the 10 000 ppm group at 52 and 77 weeks and from the 1000 ppm group
    at 77 weeks. No other effects on urinalysis measurements were
    observed in either sex at any dose level, and the decrease in pH was
    not considered to be a toxic effect of ethephon treatment.

         Ethephon was determined to be a potent inhibitor of plasma ChE
    activity with dose-related inhibition (35-41 and 65-71% in the 1000
    and 10 000 ppm male dose groups, respectively, and 18-24, 41-61, and
    74-76% in the 100, 1000, and 10 000 ppm female dose groups,
    respectively). Similar results were observed in erythrocyte ChE
    activity measurements (35-36 and 70-72% in the 1000 and 10 000 ppm
    male dose groups, respectively, and 21-36 and 60-74% in the 1000 and
    10 000 ppm female dose groups, respectively). This inhibition was,
    however, not considered to be detrimental to the animals based on
    the lack of other findings consistent with ChE inhibition. Ethephon
    treatment did not cause biologically significant inhibition of brain
    ChE at any dietary concentration used in this study (4-18%).
    Ethephon was not considered to be carcinogenic since no neoplasms
    resulted from the treatment. Two tumour types in males and two types
    in females were observed at a frequency greater than 5% (males:
    hepatocellular adenoma 6/69, 10/69, 4/70, 8/70 and lung adenoma
    2/69, 5/70, 14/70, 6/70; females: thymic region lymphosarcoma 1/68,
    2/19, 3/16, 5/68 and lung adenoma 7/70, 4/69, 7/69, 7/70 at dose
    levels of 0, 100, 1000, or 10 000 ppm, respectively). Only lung
    adenomas incidences in the 1000 ppm males were statistically
    increased over the controls. Based on no dose relation, common
    occurrence of lung adenomas in this mouse strain and that the
    adenomas were neither larger nor tended toward malignancy more than
    in other groups, it was concluded that the increase in lung adenomas
    in males was not treatment-related. Based on inhibition of
    erythrocyte ChE activity, the NOAEL was 100 ppm equal to 14 and 17
    mg/kg bw/day in males and females, respectively (Miller, 1988).

    Rats

         Male and female Sprague-Dawley CD rats (55/sex/group), received
    diets containing ethephon (purity 75.6%) at concentrations of 0, 30,
    300, or 3000 ppm for 104 weeks, equal to 0, 1.2, 12.5, or 129 mg/kg
    bw/day (males) and 0, 1.6, 16, or 171 mg/kg bw/day (females).

         Cholinesterase activity was consistently inhibited in plasma
    (22-31% at 30 ppm, 46-62% at 300 ppm and 45-67% at 3000 ppm in males
    and 29-38% at 30 ppm, 51-58% at 300 ppm and 59-66% at 3000 ppm in
    females). Similar results were obtained on erythrocytes (42-56% at
    300 ppm and 68-80% at 3000 ppm in males and 47-56% at 300 ppm and
    59-79% at 3000 ppm in females). Brain cholinesterase activity was
    not affected by ethephon (0-10%). Evaluation of all other parameters
    did not reveal any findings which could be attributed to the test
    material. Ethephon was not found to be carcinogenic in doses up to
    3000 ppm equal to 129 and 171 mg/kg bw/day in males and females,
    Based on inhibition of erythrocyte ChE activity, the NOAEL was 30
    ppm equal to 1.2 and 1.6 mg/kg bw/day in males and females,
    respectively (Reno  et al., 1978).

         Four groups of 90-100 Sprague-Dawley CD rats/sex/dose were fed
    diets containing ethephon (purity 71%) at concentrations of 0, 300,
    3000, 10 000, or 30 000 ppm for 97 weeks (males) or 104 weeks
    (females), equal to 0, 13, 131, 446, or 1420 mg/kg bw/day (males)
    and 0, 16, 161, 543, or 1790 mg/kg bw/day (females). The additional
    10 animals/sex in the 0, 10 000, and 30 000 ppm groups were
    maintained on control diet for 4 weeks following a 12-month exposure
    period to determine recovery of altered measurements. Data on
    homogeneity and stability of the diet were within acceptable ranges.

         Treatment-related alterations were observed at dietary
    concentrations of 10 000 and 30 000 ppm. These changes included an
    increased incidence of semi-solid faeces (males, 30 000 ppm),
    depressed body weight and weight gain, decreased efficiency of food
    utilization, decreased serum glucose (30 000 ppm group only), dose-
    related alterations in urinalysis measurements, particularly
    decreased urine pH (attributed to the highly acidic nature of the
    test material), and an increase in absolute (15% in females, 30 000
    ppm) and relative kidney weight (31% in females, 30 000 ppm). For
    animals treated with 3000 ppm ethephon or lower, no signs of
    toxicity were seen. Plasma and erythrocyte ChE activities were
    statistically and dose-dependently inhibited at all dose levels. In
    plasma from males, the inhibition ranged from 17-44, 27-47, 38-67,
    and 45-56% at 300, 3000, 10 000, and 30 000 ppm, respectively, and
    in plasma from females from 15-27, 37-59, 47-65, and 56-72% at 300,
    3000, 10 000, and 30 000 ppm, respectively. In erythrocytes from
    males, the inhibition ranged from 4-10, 39-47, 65-81, and 83-87% at
    300, 3000, 10 000, and 30 000 ppm, respectively, and in erythrocytes
    from females from 9-19, 43-63, 72-79, and 82-86% at 300, 3000,

    10 000, and 30 000 ppm, respectively. Inhibition of brain
    cholinesterase activity (< 9%) was not considered biologically
    significant. Carcinogenicity was not demonstrated. Animals from the
    10 000 and 30 000 ppm dose groups, maintained under control
    conditions for 4 weeks following 52-week exposure, showed recovery
    of all altered measurements. Complete recovery to control values
    was, however, not observed for body weight and plasma and
    erythrocyte ChE activity.

         Based on decreased body weight, weight gain, efficiency of food
    utilization, and increased absolute and relative kidney weight, the
    author concluded that the NOAEL was 3000 ppm, equal to 131 and 161
    mg/kg bw/day in males and females, respectively. The ChE inhibition
    was not considered detrimental to the animals based on the lack of
    other findings in both sexes consistent with ChE inhibition (Miller,
    1989). However, based on inhibition of erythrocyte ChE activity, the
    Meeting concluded that the NOAEL was 300 ppm, equal to 13 and 16
    mg/kg bw/day in males and females, respectively.

    Reproduction studies

    Rats

         Male and female Crl:CD(SD)BR Sprague-Dawley weanling rats
    (28/sex/group in the F0 generation) were exposed for 10 weeks to
    ethephon (purity 71.3%) at dietary concentrations of 0, 300, 3000,
    or 30 000 ppm, equal to 0, 22, 220, or 2260 mg/kg bw/day in F0
    males and 0, 25, 260, or 2570 mg/kg bw/day in F0 females and 0,
    20, 200, or 2220 mg/kg bw/day in F1b males and 0, 24, 245, or 2520
    mg/kg bw/day in F1b females. The animals were randomly paired
    within dose groups for a 3-week mating period to produce the F1a
    generation. Exposures continued through mating, gestation,
    parturition and lactation. At weaning on lactational day 21, 28
    F1a weanlings/sex/group were randomly selected to produce the F2
    generation and were exposed to the same dietary concentration of
    ethephon as their parents for 10 weeks. In addition, 10 F1a
    weanlings/sex/dose were randomly selected for necropsy and
    examination of gross lesions. At least 10 days after weaning of the
    F1a litters, the F0 parents were paired again for 3 weeks to
    produce the F1b generation. Exposures continued through mating,
    gestation, parturition and lactation. After the F1b pups were
    weaned, the F0 parental animals were necropsied and high-dose and
    control animals examined for histopathologic lesions. At the time of
    weaning of the F1b litters, the decision was made to use the F1b
    generation to produce the F2 generation and the F1a animals (who
    had completed a 10-week exposure) were euthanized and discarded.
    Twenty-eight F1b weanlings/sex per group were randomly selected
    and exposed to the same dietary concentrations of ethephon as their
    parents for 10 weeks. In addition, 10 randomly selected F1b
    weanlings/sex/dose were necropsied and examined for gross lesions.

    After their pre-breed exposure, F1b parental animals were paired
    as described above to produce the F2a and F2b generations.
    Mating, gestation, lactation, necropsy of the F1b parents and
    selected F2a and F2b weanlings were performed as described above
    except that no F2 animals were selected as parents. Non-selected
    F1a, F1b, F2a and F2b pups were euthanized and discarded
    after the necropsy of their selected littermates.

         During the 10-week pre-breed exposure, F0 males and females
    at 30 000 ppm exhibited consistently reduction of body weight and
    weight gain and increased incidence of loose faeces. Females at 3000
    ppm showed reduced food consumption during the 1st, 3rd and 6th
    weeks of exposure. At the F0 breed to produce F1a litters,
    gestational parameters were unaffected by treatment. Significant
    reductions in gestational body weights and lactational body weights
    were observed at 30 000 ppm. The F1a litters exhibited reduced
    body weights per litter at 30 000 ppm. During the second breeding of
    the F0 animals to produce F1b litters, gestational and
    lactational body weights were reduced at 30 000 ppm. An increased
    number of stillborn pups was observed at 30 000 ppm. F1b pup body
    weights per litter were reduced at 30 000 ppm and F1b pup deaths
    were increased at 3000 and 30 000 ppm.

         There were no treatment-related lesions observed in the
    necropsy of F1a and F1b pups which died during lactation, of
    randomly selected F1a and F1b pups or of F0 adults. There were
    also no treatment-related lesions observed in the histopathologic
    examination of selected organs from high-dose and control F0
    adults. While terminal body weight was reduced in F0 males and
    females at 30 000 ppm, absolute organ weights were unaffected by
    treatment. Brain weight relative to body weight was increased for
    F0 males and females at 30 000 ppm.

         During the 10-week exposure of the F1a animals, males at 3000
    and 30 000 ppm exhibited reductions in body weight, weight gain and
    food consumption. F1a females at 300, 3000, and 30 000 ppm
    exhibited significantly reduced body weight throughout the 10-week
    exposure, and significantly reduced body-weight gain at 3000 and
    30 000 ppm. Both males and females at 30 000 ppm exhibited increased
    incidences of loose faeces. Since the F1b generation was selected
    to produce the F2 generation, selected F1b animals were also
    subjected to a 10-week pre-breed exposure and F1a animals were
    euthanized and discarded after their 10-week exposure. During this
    period, F1b males and females at 30 000 ppm exhibited reduced body
    weight, weight gain and food consumption as well as increased
    incidences of loose faeces. Weight gain was reduced in F1b males
    and females at 3000 ppm as well. In F1b males, an increased
    incidence of loose faeces was observed at 3000 ppm.

         At the F1b breeding to produce F2a litters, gestational
    parameters were unaffected by treatment. Maternal gestational body
    weight and lactational body weight at 30 000 ppm was reduced. F2a
    pup body weights per litter were reduced at 30 000 ppm. Perinatal
    deaths and lactational survival were unaffected by treatment. During
    the second breeding of the F1b animals to produce F2b litters,
    maternal F1b gestational body weight and lactational body weight
    at 30 000 ppm were reduced. The number of stillborn F2b pups and
    perinatal deaths were increased at 30 000 ppm. F2b pup body
    weights per litter were reduced at 3000 and 30 000 ppm.

         There were no treatment-related lesions observed in the
    necropsy of F2a and F2b pups which died during lactation, of
    randomly selected F2a and F2b pups (10/sex/dose) or of F1b
    adults. There were also no treatment-related lesions observed in the
    histopathologic examination of selected organs from high-dose and
    control F1b adults. Terminal body weight was reduced in F1b
    males and females at 30 000 ppm. Brain weight relative to body
    weight and ovaries/testes weight relative to body weight were
    increased for F1b males and females at 30 000 ppm; brain weight
    relative to body weight was also increased in F1b parental adults
    at 3000 ppm.

         Based on reduced food intake, body weight and body weight gain,
    the NOAEL for maternal toxicity and for filial toxicity was 300 ppm,
    equal to 22 and 25 mg/kg bw/day in males and females, respectively.
    There was no adverse effect on reproduction at the highest dose
    tested of 30 000 ppm, equal to 2220 and 2520 mg/kg bw/day in males
    and females, respectively (Neeper-Bradley & Tyl, 1990).

    Special studies on delayed cutaneous hypersensitivity

         Evaluation of the delayed cutaneous hypersensitivity of
    ethephon (purity 72%) was performed in young adult albino Dunkin-
    Hartley guinea-pigs (10 animals/sex/group), allocated in one test
    article-control group (induction with vehicle and challenge with
    test article), one treated group (induction and challenge with test
    article) and one positive control group (induction and challenge
    with DNCB). Induction was performed by 3 series of 2 x 0.1 ml
    intradermal injections (Freund's complete adjuvant (50% V/V in
    water), ethephon (0.75 V/V in water), and a 1:1 mixture of the two
    solutions), or by topical occlusive route for 48 hours with 0.5 ml
    of ethephon (50% V/V in water). During challenge, the topical
    occlusive application was performed with 0.5 ml ethephon (35% V/V in
    water) or 0.5 ml of 1-chloro-2,4-dinitrobenzene (DNCB) (0.05% W/W in
    1.2 propylene glycol). The cutaneous macroscopic examinations were
    performed according to the scale of Magnusson & Kligman after 24 and
    48 hours followed by histopathological examinations.

         Doubtful macroscopic reactions were observed in 15 out of 20
    ethephon-treated animals. Histopathological examination of these
    lesions showed images of orthoergic irritation in 9 animals.

         No reactions of cutaneous sensitization were observed in the 20
    ethephon-treated guinea-pigs but the lesions of orthoergic
    irritation noted in 9 of them may hide possible reactions of
    cutaneous sensitization (Clement, 1989).

    Special studies on delayed neurotoxicity

         Groups of 10 white Vantress chickens received by intubation
    1000 mg/kg bw/day ethephon (purity 88%) on days 1 through 5, or 1000
    mg ethephon/kg bw on day 1 and thereafter 500 mg/kg bw/day on days 2
    through 10. Two positive control groups received 60 mg/kg bw/day
    tri-o-cresyl phosphate. Two negative control groups received 300
    mg/kg bw/day of olive oil.

         Fifteen out of 40 animals died in the test groups and 8 out of
    20 in the positive control groups. Only the deaths which occurred in
    the positive control group were considered to be due to
    neurotoxicity. No clinical signs of neurotoxicity and no gross
    pathology was observed in any of the necropsied chickens.
    Microscopic examination showed no cytopathologic changes in the
    spinal cord or sciatic nerve of the animals receiving ethephon.
    Administration of tri-o-cresyl phosphate caused clinical signs of
    neurotoxicity and some spinal axonal dystrophy in 10 chickens and
    sciatic neuropathy in one chicken. The Meeting concluded that there
    was no evidence of delayed neurotoxicity at doses up to 1500 mg/kg
    bw/day (Weatherholtz & Shott, 1970).

         Groups of 15-30 white leghorn chickens received a single oral
    dose of 0, 3160, or 3850 mg/kg bw ethephon (purity 71%). A positive
    control group received 500 mg/kg bw tri-o-tolyl phosphate orally.
    Twenty-one days following dosing, all surviving birds (21) were
    treated orally with a single dose of 2370 mg/kg bw ethephon.

         Twenty-eight of thirty birds in the 3850 mg/kg group were found
    dead within 24 hours after the first dose. One additional mortality
    was recorded in this group on test day 8. Ten of thirty birds in the
    3160 mg/kg group were found dead within 24 hours after the first
    dose. One bird from this group was found dead within 48 hours after
    the second dose. Signs of lethargy and anorexia were present
    following dosing. Complete recovery of all surviving birds was seen
    during both 21-day test periods. There were no signs of locomotor
    disturbances or other clinical signs of delayed neurotoxicity among
    any of the ethephon-treated chickens during the 42-day test period.
    Ethephon-treated birds exhibited decreased food intake and body
    weight loss during the test period. The positive control birds lost
    weight and exhibited behavioural signs of neurotoxicity by day 9 of

    the investigation. All positive control birds were sacrificed  in
     extremis on test day 17 or 18. Gross pathologic examination of
    birds found dead within 24 hours after dosing revealed diffuse red
    discoloration with severe dilation of the vessels in the intestinal
    tract and diffuse light grey discoloration with transparent gel
    circumscribing the crop area in all birds. Histopathology of neural
    tissues from the ethephon-treated birds revealed no changes.
    Treatment-related lesions were noted with respect to the positive
    control birds. No evidence of delayed neurotoxicity was observed in
    this study at 3160 mg/kg bw. The 3850 mg/kg bw dose could not be
    evaluated since at this high level only one bird survived the
    observation period (Fletcher, 1983).

    Special studies on embryotoxicity/teratogenicity

         Sexually mature, virgin female Charles River COBS(R) CD rats
    were acclimated for 10 days before being mated with males of the
    same strain at an age of 15 weeks. Groups of pregnant rats (25
    rats/group) were dosed orally by garage (10 ml 0.5% aqueous
    Methocel(R) suspension/kg bw) with 0, 200, 600, or 1800 mg/kg
    bw/day ethephon (purity not given) on days 6 through 19 of
    gestation.

         There were no biologically significant differences in maternal
    appearance, behaviour and body-weight gain, and there were no signs
    of fetotoxicity or teratogenicity in the 200 and 600 mg/kg bw/day
    group when compared to the control group. At 1800 mg/kg bw/day, 14
    of the 25 dams died during the treatment period and only nine
    litters with viable fetuses were available for evaluation. The NOAEL
    was 600 mg/kg bw/day, based on maternal toxicity (Rodwell, 1980).

         Male and female Crl:CD(SD)BR rats were used for breeding. Mated
    females (25/group) were treated with ethephon (purity 71.7%) by oral
    gavage at 0, 125, 250, or 500 mg/kg bw/day on days 6 through 115 of
    gestation.

         Survival rates were 100% at all dose levels and there were no
    test material-related clinical observations. There were no
    statistically significant differences in body weights of treated
    animals when compared with those of controls and no test material-
    related parental necropsy observations.

         The pregnancy rates were 92%, 84%, 88%, and 88% at 0, 125, 250,
    and 500 mg/kg bw/day, respectively. There were no significant
    differences in the number of corpora lutea or implantations,
    implantation efficiency, the number or percentage of live or
    resorbed fetuses, or mean fetal weights and no test material-related
    fetal external, soft tissue, or skeletal abnormalities.

         There was a significant increase in the total number of fetuses
    at 125 and 250 mg/kg bw/day with skeletal abnormalities such as
    reduced vertebral arches; however, there was no statistical
    difference in the percent of total fetal skeletal abnormalities.
    This observation was not considered toxicologically important
    because there was no dose-response and no increase in the total
    number or percent of fetuses in the high dose. The NOAEL for
    maternal toxicity was 500 mg/kg bw/day. There was no teratogenicity
    at the dose levels tested (Henwood, 1989).

    Rabbits

         Ethephon (purity unknown) at 0, 50, 100, or 250 mg/kg bw/day in
    water was administered orally by intubation to groups of 17 pregnant
    New Zeeland white rabbits from day 6 through day 19 of gestation.

         An increased incidence of inactive animals was noted in the
    maternal 250 mg/kg bw/day group during the treatment and post-
    treatment phases. Lower food consumption values during the treatment
    and a significantly lower maternal survival rate were also noted in
    this group. No other significant findings were noted in the maternal
    animals.

         The mean number of resorptions was higher at 100 and 250 mg/kg
    bw/day and on a per litter basis, a significantly higher incidence
    of resorption was noted in the 250 mg/kg bw/day animals. The mean
    number of live fetuses and fetal viability was lower at 100 and 250
    mg/kg bw/day. However, no statistically significant differences were
    noted. All other fetal data were comparable between the control and
    treated groups.

         The NOAEL for maternal and embryo/fetotoxicity was 50 mg/kg
    bw/day based on the lower survival rate and higher resorptions.
    There were no teratogenic effects (Weatherholtz  et al., 1981).

         Ethephon (purity 72.2%) was administered by oral gavage to
    pregnant New Zeeland white rabbits on days 7 through 19 of gestation
    at dosages of 0, 63, 125, or 250 mg/kg bw/day. The control animals
    received deionized water.

         The percent of females surviving to the scheduled necropsy was
    95, 91, 95 and 14%, for the control, 63, 125, and 250 mg/kg bw/day
    group, respectively. Test material-related clinical observations
    were seen for 17/22 females at 250 mg/kg bw/day including ataxia and
    prostration. There were no test material-related clinical
    observations at 63 or 125 mg/kg bw/day. At 250 mg/kg bw/day, but not
    at the two lower dose levels, the body weight and weight gain were
    significantly lower than those of controls.

         Parental necropsy findings, such as erosions in the stomach,
    were more frequent among the 250 mg/kg bw/day does (8 does compared
    with 2 control does).

         Pregnancy rates were 95, 95, 91, and 82% for the control, 63,
    125, and 250 mg/kg group, respectively. Post-implantation loss and
    the percent of early resorptions were considerably higher and the
    percent of live fetuses was lower at 250 mg/kg bw/day. There were no
    statistical differences in fetal body weight and no test material-
    related fetal external, soft tissue, or skeletal variations or
    malformations. The NOAEL for maternal and embryo/fetotoxicity was
    125 mg/kg bw/day. There were no teratogenic effects (Henwood, 1990).

    Special studies on genotoxicity

         Ethephon was not considered genotoxic since it was negative in
    several  in vitro and  in vivo test systems except when tested in
    the Ames test with  Salmonella typhimurium, strain TA1535. Data are
    shown in Table 2.

    Special studies on skin irritation

         In a skin irritation test, 0.5 ml of an aqueous ethephon (70%
    active ingredient) solution was placed on one intact site of the
    dorsal area of the trunk of each of 6 New Zeeland white rabbits,
    clipped a few days before dosing and trimmed just before application
    of the test material. Contact periods were 1 or 4 hours. Ethephon
    was found to be corrosive after the 4-hour contact period since
    spots of necrosis and edema were observed in 4 rabbits and contact
    erythema in 6 rabbits. After the 1-hour procedure, erythema, but no
    edema or necrosis, was observed (Myers, 1983).

    Special studies on skin sensitization

         Groups of Hartley-derived albino guinea-pigs (5/sex), received
    a patch containing 0.4 ml 25% w/v ethephon (72% active ingredient)
    water solution. The patch was applied to each animal and occluded
    for 6 hours once weekly for three consecutive weeks.
    Dinitrochlorobenzene in 100% alcohol was used as the control.
    Following a 2-week rest period, the guinea-pigs were topically
    challenged with ethephon (10% w/v in distilled water). No evidence
    of contact sensitization was observed following challenge with
    ethephon (Rush, 1989).

    Observations in humans

         A preliminary dose range study with ethephon was carried out in
    2 human volunteers. They received 5.4-120 rag/day ethephon (purity
    88%) in propylene glycol (by oral capsule, in 3 divided doses, one
    immediately after each meal) over a 7-week period. The approximate
    dosage ranged from 0.06-1.25 mg/kg bw/day.


        Table 2. Results of genotoxicity assays on ethephon
                                                                                                                          
    Test system              Test object                   Concentration     Purity      Results        Reference
                                                           of ethephon
                                                                                                                          

      In vitro

     Ames test (with and     Salmonella typhimurium        0.1-50            72.3%                      Jagannath, 1987
     without metabolic       TA1535                        µg/plate                      +(±S9)
     activation)             TA1537                                                      -(±S9)
                             TA1538                                                      -(±S9)
                             TA98                                                        -(±S9)
                             TA100                                                       -(+S9)

     DNA repair test         Rat hepatocyte primary        10-1000           71.0%       -              Barfknecht et al.,
                             culture                       µg/ml                         -              1984

     Unscheduled DNA         Rat hepatocyte                25-1000           71.3%       -              Cifone, 1988
     synthesis assay                                       µg/ml

     Chromosomal aberration  Chinese hamster ovary         502-2010          71.3%       -              Murli, 1988
     (± activat.)            cell                          µg/ml

     CHO/HGPRT mutation      Mammalian CHO-KI-             500-2500          71.0%       -              Godek et al.,
     assay (+ activat.)      BH4 cells                     µg/ml                                        1983

     CHO/HGPRT mutation      Mammalian CHO-KI-             166-5000          71,0%       -              Godek et al.,
     assay (+ activat.)      BH4 cells                     µg/ml                                        1984

     CHO/HGPRT mutation      Mammalian CHO-KI-             500-2600          72.3%       -              Young, 1988
     assay (+ activat.)      BH4 cells                     µg/ml

                                                                                                                          

    Table 2 (contd)
                                                                                                                          
    Test system              Test object                   Concentration     Purity      Results        Reference
                                                           of ethephon
                                                                                                                          

      In vivo

     Micronucleus test       Mice                          200 mg/kg         >90%        -              Sorg et al., 1981
                                                           bw

     Dominant lethal         Rats                          250-1000          ?           -              Naismith &
                                                           mg/kg bw          (>707)                     Matthews, 1979

                                                                                                                          
    

         The compound had no inhibitory activity on human plasma or
    erythrocyte ChE activity. No persistent side effects were observed
    during the course of the study. However, transient, subjective
    feelings of urinary urgency were experienced by both volunteers. A
    slight elevation in serum GPT was also observed from the 26-46th day
    of study. Laboratory studies performed two weeks following the last
    compound administration gave test results within normal biological
    limits (Reese, 1971).

         Sixteen human volunteers in good health received orally by
    capsule 0 (3 males and 3 females) or approximately 120 mg/day (5
    males and 5 females) of ethephon (divided into 3 doses) for 28 days
    (purity 10% in a powdered formulation), followed by a 14-day dose-
    free period. Based on average substance consumption and average body
    weight for the subjects, the approximate dosage was 1.5 mg/kg bw/day
    in makes and 2.2 mg/kg bw/day in females. The results indicated that
    the compound had no inhibitory effect on human plasma or erythrocyte
    cholinesterase activity. No persistent side effects were observed
    during the course of the study. However, transient subjective
    complaints of urinary urgency, sudden "onset of diarrhoea", effect
    on appetite and dyspepsia were recorded. Laboratory studies
    performed during the study and two weeks following the last dose of
    test material were, in general, within normal biological limits.
    Based on clinical symptoms, a NOAEL could not be determined (Reese,
    1972).

         Thirty human volunteers in good health received orally by
    capsule, without knowing to which group they were assigned, 0 (6
    males and 4 females) or 0.5 mg/kg bw/day (10 males and 10 females)
    of ethephon (purity 2.5% in a powdered formulation), divided into 3
    doses, for 16 days, followed by a 29-day dose-free period. Plasma
    cholinesterase activity was significantly inhibited and in a
    reversible manner (54-62% of pre-dose levels). No gross symptoms nor
    changes in haematology, clinical chemistry, or urinalysis were
    associated with the test substance administration. The NOAEL was 0.5
    mg/kg bw/day in both males and females, based on lack of inhibition
    of erythrocyte cholinesterase (Weir, 1977a).

         Twenty human volunteers in good health received orally by
    capsule, without knowing to which group they were assigned, 0 (3
    males and 3 females), 0.17 (3 males and 4 females) or 0.33 mg/kg
    bw/day (4 males and 3 females) of ethephon (purity 22% in a powdered
    formulation), divided into 3 doses, for 22 days, followed by a 14-
    day dose-free period. Plasma ChE activity was significantly and
    irreversibly inhibited (59-74% of pre-dose values). No gross
    symptoms nor changes in haematology, clinical chemistry, or
    urinalysis were associated with the test substance administration.
    The NOAEL was 0.33 mg/kg bw/day in both males and females, based on
    lack of inhibition of erythrocyte cholinesterase (Weir, 1977b).

    COMMENTS

         Following oral administration of ethephon to rats, about 90% of
    the administered radioactivity was recovered, principally in urine
    (50%), expired air (19%), and faeces (6%) during 120 hours post-
    dose. Most of the dose was recovered within 24 hours post-dose.

         After oral administration of ethephon to dogs, radioactivity
    was found in urine (40%), expired air (30%) and faeces (5%). Total
    body retention was 1%. Peak plasma and red blood cell concentrations
    were observed 2 hours after dosing. Only traces were observed after
    22 hours.

         After oral administration to rats, ethephon was excreted in
    urine and faeces as the mono- and disodium salts and some
    unidentified metabolites and metabolized to ethylene and eliminated
    in the expired air. In dogs, ethephon is partly metabolized to
    ethylene and eliminated in expired air and also excreted unchanged
    in the urine.

         In dogs dosed orally with ethephon, plasma cholinesterase
    activity was inhibited at 2 hours with recovery starting within a
    few hours. Erythrocyte cholinesterase levels responded more slowly
    with signs of recovery at 72 hours.

         Ethephon has a low oral acute toxicity in mice, rats, and
    rabbits. WHO has classified ethephon as unlikely to represent acute
    hazard in normal use. Ethephon is corrosive to the skin of rabbits.

         In a four-week study in mice at dietary concentrations of 0,
    30, 100, 300, 1000 or 3000 ppm, the NOAEL was 300 ppm (equal to 51
    mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
    activity.

         In a four-week study in rats at dietary concentrations of 0,
    625, 1250, 2500, 5000 or 10 000 ppm, the NOAEL was 625 ppm (equal to
    52 mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
    activity.

         In a one-year study in dogs at dietary concentrations of 0,
    100, 300, 1000 or 2000 ppm, the NOAEL was 1000 ppm (equal to 27
    mg/kg bw/day), based on soft stools and changes in body and spleen
    weight. However, cholinesterase activities were not determined.

         In a two-year study in dogs at dietary concentrations of 0, 30,
    300, or 1500 ppm, the NOAEL was 30 ppm (equal to 0.86 mg/kg bw/day),
    based on inhibition of erythrocyte cholinesterase activity and
    smooth muscle hypertrophy in the stomach and small intestine.

         In two 78-week studies in mice at dietary concentrations of 0,
    30, 100, 300, 1000 or 10 000 ppm, the NOAEL was 100 ppm (equal to 14
    mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
    activity. There was no evidence of carcinogenicity.

         In two 104-week studies in rats at dietary concentrations of 0,
    30, 300, 3000, 10 000 or 30 000 ppm, the NOAEL was 30 ppm (equal to
    1.2 mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
    activity. There was no evidence of carcinogenicity.

         Brain cholinesterase was not depressed in any study.

         In a two-generation reproduction study in rats at dietary
    concentrations of 0, 300, 3000 or 30 000 ppm, the NOAEL for maternal
    and filial toxicity was 300 ppm (equal to 22 mg/kg bw/day), based on
    reduced food intake, body weight and weight gain. There was no
    adverse effect on reproduction.

         In two studies in hens for delayed neurotoxicity, no evidence
    of delayed neurotoxicity was observed.

         In two oral teratogenicity studies in rats at dose levels of 0,
    125, 200, 250, 500, 600, or 1800 mg/kg bw/day, the NOAEL was 600
    mg/kg bw/day, based on maternal toxicity. There were no teratogenic
    effects.

         In two teratogenicity studies in rabbits at oral dose levels of
    0, 50, 63, 100, 125, or 250 mg/kg bw/day, the NOAEL was 50 mg/kg
    bw/day, based on maternal and embryo/fetotoxicity. There were no
    teratogenic effects.

         After reviewing the  in vitro and  in vivo genotoxicity data,
    the Meeting concluded that there was no evidence of genotoxicity.

         In 16 male and female human volunteers treated orally with 0 or
    120 mg/day (divided into 3 doses) of ethephon (approximately 1.5 and
    2.2 mg/kg bw/day in males and females, respectively) for 28
    consecutive days, no significant inhibitory effect on human plasma
    or erythrocyte cholinesterase activity was observed. Subjective
    complaints of urinary urgency, sudden onset of diarrhoea, effect on
    appetite and dyspepsia were recorded. Based on clinical symptoms, a
    NOAEL could not be determined.

         In 30 male and female human volunteers treated orally with 0 or
    0.5 mg/kg bw/day of ethephon (divided into 3 doses) for 16
    consecutive days, plasma cholinesterase activity was inhibited but
    recovered within the recovery period of 29 days. The NOAEL was 0.5
    mg/kg bw/day in both males and females, based upon the lack of
    inhibition of erythrocyte cholinesterase.

         In 20 male and female human volunteers receiving 0, 0.17 or
    0.33 mg/kg bw/day of ethephon orally (divided into 3 doses) for 22
    consecutive days, plasma cholinesterase activity was inhibited and
    did not recover within the recovery period of 14 days. The NOAEL was
    0.33 mg/kg bw/day in both males and females, based upon the lack of
    inhibition of erythrocyte cholinesterase.

         An ADI of 0-0.05 mg/kg bw was established, based on the NOAEL
    in the 16-day study in humans of 0.5 mg/kg bw/day, using a 10-fold
    safety factor.

    TOXICOLOGICAL EVALUATION

    Level causing no toxicological effect

         Mouse:    100 ppm, equal to 14 mg/kg bw/day (78-week study)

         Rat:      30 ppm, equal to 1.2 mg/kg bw/day (104-week study)

         Dog:      30 ppm, equal to 0.86 mg/kg bw/day (two-year study)

         Humans:   0.5 mg/kg bw/day (16-day study).

    Estimate of acceptable daily intake for humans

                   0-0.05 mg/kg bw.

    Studies which will provide information valuable in the continued
    evaluation of the compound

         The Meeting noted that ethephon is a dibasic phosphonic acid
    and therefore not able to phosphorylate hydrolases at the serine
    residue. However,  in vivo data showed inhibition of plasma and
    erythrocyte, but not brain, cholinesterase. Neither data with the
    pure compound nor  in vitro studies were available. The Meeting
    considered that these effects on cholinesterases need clarification
    and recommended re-evaluation of the compound in 1995.

         Further observations in humans.

    REFERENCES

    Barfknecht, T.R., Naismith, R.W. & Matthews, R.J. (1984). Rat
    hepatocyte primary culture/DNA repair test. Unpublished report No.
    PH 311-UC-002-84 from Pharmacon Research International, Inc.,
    Waverly, Pennsylvania 18471, USA. Submitted to WHO by Rhône-Poulenc,
    Secteur Agro, Lyon, France.

    Cifone, M.A. (1988). Mutagenicity test on ethephon in the rat
    primary hepatocyte unscheduled DNA synthesis assay. Unpublished
    Report No. 10065-0-447 from Hazleton Laboratories America, Inc.,
    5516 Nicholson Lane, Suite 400, Kensington, Maryland 20895, USA.
    Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Clement, C. (1989). Test to evaluate the sensitizing potential in
    the guinea-pig. Guinea-pig maximization test. Unpublished report No.
    903326 from Hazleton France, Les Oncins, B.P. 118 -69210 L'Arbresle,
    France. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon,
    France.

    Fletcher, D.W. (1983). 42-Day neurotoxicity study with ethephon in
    mature white leghorn chickens. Unpublished and unnumbered report
    (project No. 83 DN 102) from Bio-life Associates, Ltd. Route 3, Box
    156, Neilisville, Wisconsin 54456, USA. Submitted to WHO by Rhône-
    Poulenc, Secteur Agro, Lyon, France.

    Godek, E.G., Naismith, R.W. & Matthews, R.J. (1983). CHO/HGPRT,
    mammalian cell forward gene mutation assay. Unpublished report No.
    PH-314-UC-003-83 from Pharmacon Research International, Inc.,
    Waverly, Pennsylvania 18471, USA. Submitted to WHO by Rhône-Poulenc
    Secteur Agro, 14, 20, Rue Pierre Baizet, BP 9163 - 69263 Lyon Cedex
    09, France.

    Godek, E.G., Naismith, R.W. & Matthews, R.J. (1984). CHO/HGPRT,
    mammalian cell forward gene mutation assay. Unpublished report No.
    PH-314-UC-001-84 from Pharmakon Research International, Inc.,
    Waverly, Pennsylvania 18471, USA. Submitted to WHO by Rhône-Poulenc
    Secteur Agro, 14, 20, Rue Pierre Baizet, BP 9163 - 69263 Lyon Cedex
    09, France.

    Hamada, N.N. (1989). One-year oral toxicity study in Beagle dogs
    with ethephon(R). Unpublished and unnumbered report (Project No.
    HLA 400-722) from Hazleton Laboratories America Inc., 9200 Leesburg
    Turnpike, Vienna, Virginia 22180, USA. Submitted to WHO by Rhône-
    Poulenc, Secteur Agro, Lyon, France.

    Hardy, I.A.J., Chem, C., Marshall, I.R. & Outram, J.R. (1990). Plant
    growth regulators: ethephon. Spectroscopic identification of
    metabolites from a 14C-ethephon ADME study in the rat. Unpublished
    report No. D. Ag. 1523 from Rhône-Poulenc Agriculture Limited,
    Fyfied Road, Ongar, Essex, United Kingdom. Submitted to WHO by
    Rhône-Poulenc, Secteur Agro, Lyon, France.

    Henwood, S.M. (1989). Teratology study with ethephon technical-base
    250 in rats. Unpublished and unnumbered report (Project No. HLA
    6224-125) from Hazleton Laboratories America Inc., 3301 Kinsman
    Boulevard., P.O. Box 7545, Madison, Wisconsin 53707, USA. Submitted
    to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Henwood, S.M. (1990). Teratology study with ethephon technical-base
    250 in rabbits. Unpublished and unnumbered report (Project No. HLA
    6224-158) from Hazleton Laboratories America Inc., 3301 Kinsman
    Boulevard., P.O. Box 7545, Madison, Wisconsin 53707, USA. Submitted
    to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Holsing, G.C. (1969). Acute oral - Mice, five compounds. Unpublished
    and unnumbered report (Project No. 141-197) from Hazleton
    Laboratories, Inc., TRW Life Sciences Center, P.O. Box 30, Falls
    Church, Virginia 22046, USA. Submitted to WHO by Rhône-Poulenc,
    Secteur Agro, Lyon, France.

    Holsing, G.C. (1969). Three-week repeated dermal application -
    rabbits. Unpublished and unnumbered report (Project No. 141-171)
    from Hazleton Laboratories, Inc., TRW Life Sciences Center, P.O. Box
    30, Falls Church, Virginia 22046, USA. Submitted to WHO by Rhône-
    Poulenc, Secteur Agro, Lyon, France.

    Jagannath, D.R. (1987). Mutagenicity test on ethephon Base 250 in
    the Ames  Salmonella/microsome reverse mutation assay. Unpublished
    report No. 10065-0-401 from Hazleton Laboratories America, Inc.,
    5518 Nicholson Lane, Suite 400, Kensington, Maryland 20895, USA.
    Submitted to WHO by Rhône-Poulenc Secteur Agro, 14, 20, Rue Pierre
    Baizet, BP 9163 - 69263 Lyon Cedex 09, France.

    Miller, J.P. Van & Troup, C.M. (1986a). Twenty-eight day dietary
    toxicity study with ethephon in mice. Unpublished report No. 48-139
    from Bushy Run Research Center, R.D. 4, Mellon Road, Export,
    Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur
    Agro, Lyon, France.

    Miller, J.P. Van & Troup, C.M. (1986b). Twenty-eight day dietary
    toxicity study with ethephon in mice study II. Unpublished report
    No. 49-4 from Busily Run Research Center, R.D. 4, Mellon Road,
    Export, Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc,
    Secteur Agro, Lyon, France.

    Miller, J.P. Van & Troup, C.M. (1986c). Twenty-eight day dietary
    toxicity study with ethephon in rats. Unpublished report No. 48-123
    from Bushy Run Research Center, R.D. 4, Mellon Road, Export,
    Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur
    Agro, Lyon, France.

    Miller, J.P. Van & Troup, C.M. (1986d). Twenty-eight day dietary
    toxicity study with ethephon in rats Study No. II. Unpublished
    report No. 49-3 from Bushy Run Research Center, R.D. 4, Mellon Road,
    Export, Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc,
    Secteur Agro, Lyon, France.

    Miller, J.P. Van (1988). Lifetime dietary oncogenicity study with
    ethephon in albino mice. Unpublished report No. 51-502 from Bushy
    Run Research Center, R.D. 4, Mellon Road, Export, Pennsylvania
    15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon,
    France.

    Miller, J.P. Van (1989). Lifetime dietary combined chronic toxicity
    and oncogenicity study with ethephon in albino rats. Unpublished
    report No. 51-501 from Bushy Run Research Center, R.D. 4, Mellon
    Road, Export, Pennsylvania 15632, USA. Submitted to WHO by Rhône-
    Poulenc, Secteur Agro, Lyon, France.

    Murli, H. (1988). Mutagenicity test on ethephon base 250 in an  in
     vitro cytogenetic assay measuring chromosomal aberration
    frequencies in Chinese hamster ovary (CHO) cells. Unpublished report
    No. 10065-0-437 from Hazleton Laboratories America, Inc., 5516
    Nicholson Lane, Suite 400, Kensington, Maryland 20895, USA.
    Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Myers, R.C. (1983). Ethephon base 250, primary skin irritancy
    (D.O.T.). Unpublished report No. 46-11 from Bushy Run Research
    Center, R.D. 4, Mellon Road, Export, Pennsylvania 15632, USA.
    Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Myers, R.C. (1984). Ethephon base 250, acute peroral toxicity study.
    Unpublished report No. 47-49 from Bushy Run Research Center, R.D. 4,
    Mellon Road, Export, Pennsylvania 15632, USA. Submitted to WHO by
    Rhône-Poulenc, Secteur Agro, Lyon, France.

    Myers, R.C. (1989). Ethephon base 250, acute percutaneous toxicity
    study. Unpublished report No. 46-122 from Bushy Run Research Center,
    R.D. 4, Mellon Road, Pennsylvania 15632, USA. Submitted to WHO by
    Rhône-Poulenc, Secteur Agro, Lyon, France.

    Nachreiner, D.J. & Klonne, D.R. (1989). Ethephon base 250, acute
    aerosol inhalation toxicity test in rats. Unpublished report No. 52-
    580 from Bushy Run Research Center, R.D. 4, Mellon Road, Export,
    Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur
    Agro, Lyon, France.

    Naismith, R.W. & Matthews, R.J. (1979). Dominant lethal study.
    Unpublished report No. 56375 from Pharmakon Laboratories, 1140
    Quincy Avenue, Scranton, Pennsylvania 18510, USA. Submitted to WHO
    by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Neeper-Bradley, T.L. & Tyl, R.W. (1990). Two-generation reproduction
    study in CD albino rats exposed to ethephon by dietary inclusion.
    Unpublished report No. 51-539 from Bushy Run Research Center, 6702
    Mellon Road, Export, Pennsylvania 15632-8902, USA. Submitted to WHO
    by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Reno, F.E & Voelker, R.W. (1977). A two-year dietary study in dogs,
    ethrel. Unpublished and unnumbered report (Project No. 141-260) from
    Hazleton Laboratories America Inc., 9200 Leesburg Turnpike, Vienna,
    Virginia 22180, USA. Submitted to WHO by Rhône-Poulenc, Secteur
    Agro, Lyon, France.

    Reno, F.E, Serota, D.G., & Voelker R.W. (1978). 104-Week chronic
    toxicity study in rats. Unpublished and unnumbered report (Project
    No. 141-263) from Hazleton Laboratories America Inc., 9200 Leesburg
    Turnpike, Vienna, Virginia 22180, USA. Submitted to WHO by Rhône-
    Poulenc, Secteur Agro, Lyon, France.

    Reese, W.H. (1971). Preliminary dose range study in two human
    volunteers. Unpublished and unnumbered report (project No. 1223)
    from Bionetics Research Laboratories, Division of Litton Industries,
    Bionetics Research Laboratories, Inc. 7300 Pearl Street, Bethesda,
    Maryland 20014, USA. Submitted to WHO by Rhône-Poulenc, Secteur
    Agro, Lyon, France.

    Reese, W.H. (1972). Evaluation of ethrel in human volunteers.
    Unpublished and unnumbered report (project No. 7223) from Bionetics
    Research Laboratories, Division of Litton Industries, Bionetics
    Research Laboratories, Inc. 7300 Pearl Street, Bethesda, Maryland
    20014, USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon,
    France.

    Rodwell, D.E. (1980). Teratology study in rats. Unpublished report
    No. 369-042 from International Research and Developmental
    Corporation, Mattawan, Michigan 49071, USA. Submitted to WHO by
    Rhône-Poulenc, Secteur Agro, Lyon, France.

    Rush, R.E. (1989). Dermal sensitization study in guinea-pigs with
    Base A-250. Unpublished and unnumbered report (study No. SLS
    3147.44) from Springborn Laboratories, Inc. Mammalian Toxicology
    Division, 553 North Broadway, Spencerville, Ohio 45887, USA.
    Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Savage, E.A. (1990). 14C-ethephon: absorption, distribution,
    metabolism, and excretion in the rat. Unpublished report No. 68/103
    & P89/366 from Hazleton UK, North Yorkshire HG3 1PY, United Kingdom.
    Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Sorg, R.M., Naismith, R.W. & Matthews, R.J. (1981). Genetic
    toxicology micronucleus test (MNT). Unpublished report No. PH 309A-
    UC-001-81 from Pharmakon Laboratories, Waverly, Pennsylvania 18471,
    USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Stephen, W. & Walker D. (1971). Metabolism of 14C-ethephon in the
    dog. Unpublished and unnumbered report from Hazleton Laboratories
    America Inc., 9200 Leesburg Turnpike, Vienna, Virginia 22180, USA.
    Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Stephen, W. & Stanovick, R.P. (1971). Identification of 14C-
    ethephon metabolites in the dog. Unpublished and unnumbered report
    from Hazleton Laboratories America Inc., 9200 Leesburg Turnpike,
    Vienna, Virginia 22180, USA. Submitted to WHO by Rhône-Poulenc,
    Secteur Agro, Lyon, France.

    Voss, K.A. & Becci, P.J. (1985). 78-Week oncogenic evaluation in
    Swiss albino mice. Unpublished and unnumbered report (study no.
    5754) from Food and Drug Research Laboratories, Inc, Route 17C, P.O.
    Box 107, Waverly, NY 14892-0107 607 565-8131, USA. Submitted to WHO
    by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Weatherholtz, W.M. (1980). Acute oral toxicity study in rabbits.
    Unpublished and unnumbered report (Project No. 400-630) from
    Hazleton Laboratories America, Inc., 9200 Leesburg Turnpike, Vienna,
    Virginia 22180, USA. Submitted to WHO by Rhône-Poulenc, Secteur
    Agro, Lyon, France.

    Weatherholtz, W.M. & Shott, L.D. (1970). Neurotoxicity Study - Hens,
    Ethrel, formulated, Etrel, technical. Unpublished and unnumbered
    report (Project No. 141-218) from Hazleton Laboratories, Inc., TRW
    Life Sciences Center, P.O. Box 30, Falls Church, Virginia 22046,
    USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Weatherholtz, W.M, Wolfe, G.W. & Durloo, R.S. (1981). Teratology
    study in rabbits, technical ethephon. Unpublished and unnumbered
    report (Project No. 400-635) from Hazleton Laboratories America,
    Inc., 9200 Leesburg Turnpike, Vienna, Virginia 22180, USA. Submitted
    to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Weir, R.J. (1977a). Evaluation of ethephon in human volunteers.
    Unpublished and unnumbered report (project No. 2416) from Litton
    Bionetics, Inc. 5516 Nicholson Lane, Kensington, Maryland 20795,
    USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    Weir, R.J. (1977b). Evaluation of ethephon in human volunteers.
    Unpublished and unnumbered report (project No. 2476) from Litton
    Bionetics, Inc. 5516 Nicholson Lane, Kensington, Maryland 20795,
    USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.

    WHO (1992). The WHO recommended classification of pesticides by
    hazard and guidelines to classification 1992-1993 (WHO/PCS/92.14).
    Available from the International Programme on Chemical Safety, World
    Health Organization, Geneva, Switzerland.

    Young, R.R. (1988). Mutagenicity test on ethephon base 250 in the
    CHO/HGPRT forward mutation assay. Unpublished report No. 10065-0-435
    from Hazleton Laboratories America, Inc. 5516 Nicholson Lane, Suite
    400, Kensington, Maryland 20895, USA. Submitted to WHO by Rhône-
    Poulenc, Secteur Agro, Lyon, France.


    See Also:
       Toxicological Abbreviations
       Ethephon (Pesticide residues in food: 1977 evaluations)
       Ethephon (Pesticide residues in food: 1978 evaluations)
       Ethephon (Pesticide residues in food: 1983 evaluations)
       Ethephon (JMPR Evaluations 2002 Part II Toxicological)