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    ETHOXYQUIN       JMPR 1998

    First draft prepared by
    I. Dewhurst
    Pesticides Safety Directorate, Ministry of Agriculture, 
    Fisheries and Food,
    Mallard House, Kings Pool, York, United Kingdom


         Explanation 
         Evaluation for acceptable daily intake 
                   Biochemical aspects 
                        Absorption, distribution, and excretion
                        Biotransformation 
                        Effects on enzymes and other biochemical
                             parameters
                   Toxicological studies 
                        Acute toxicity 
                        Short-term studies of toxicity 
                        Long-term studies of toxicity and carcinogenicity
                        Genotoxicity 
                        Reproductive toxicity 
                             Multigeneration reproductive toxicity
                             Developmental toxicity 
                   Observations in humans
         Comments 
         Toxicological evaluation 
         References 


    Explanation

         Ethoxyquin was previously evaluated by the Joint Meeting in 1969
    (Annex 1, reference 12), when an ADI of 0-0.06 mg/kg bw was
    established on the basis of the NOAELs in a long-term feeding study in
    dogs and a study of reproductive toxicity in rats. The compound was
    reviewed at the present meeting within the CCPR periodic review
    programme. This monograph summarizes new data and data not previously
    reviewed on ethoxyquin and relevant data from the previous monograph
    (Annex 1, reference 13).


    Evaluation for Acceptable Daily Intake

    1.  Biochemical aspects

     (a)  Absorption, distribution, and excretion

         Data from the 1950s were summarized briefly in the 1969 JMPR
    monograph (Annex 1, reference 13). In pretreated rats, equal amounts
    of a 1.5-mg dose were excreted in urine and faeces, with a total of
    64% excreted in 48 h; about 1% of the administered radiolabel was
    exhaled as carbon dioxide. The liver, kidneys, fat, and skeletal

    muscle contained the highest concentrations of residues (1-5 mg/kg).
    Newborn rats had tissue concentrations of 0.12-0.21 mg/kg, indicating
    some placental transfer; similar concentrations were found in rat
    milk, but maternal tissue concentrations were not available for
    comparison. In dogs, excretion occurred primarily in the urine as
    unidentified metabolites. In chickens, 99% of the radiolabel from an
    oral dose of ethoxyquin was excreted as metabolites within 48 h; after
    12 weeks of administration of about 130 ppm in the diet, the tissue
    concentrations were low (0.1 mg/kg) and declined rapidly after
    withdrawal of the treated diet. 

         The absorption, distribution, and excretion of ethoxyquin were
    investigated in groups of three male Fischer 344 rats and B6C3F1
    mice, approximately eight weeks old, which received single doses of
    ethoxyquin (purity, 90%) containing [3-14C]ethoxyquin (purity, 96%)
    by gavage at 2.5 (rats only), 25, or 250 mg/kg bw or single
    intravenous doses of 25 mg/kg bw. The substance was administered in a
    1:1:8 mixture of ethanol:emulphor EL620:water at a volume of 1 ml/kg
    bw, equivalent to 25-50 Ci/kg. Urine, faeces, and air were sampled at
    various times between 4 and 72 h. The concentrations in liver, kidney,
    blood, muscle, skin, and adipose tissue were determined by sequential
    kills between 0.25 and 72 h. Additional groups of four rats were used
    to determine blood and plasma concentrations in the jugular vein
    0.08-24 h after a dose of 25 mg/kg bw and to determine tissue, urine,
    and faecal concentrations after six doses of 25 or 250 mg/kg bw.
    Radiolabel was determined by liquid scintillation counting; faecal
    samples were first powdered and combusted. The concentrations of
    parent ethoxyquin in the samples were determined by high-performance
    liquid chromatography (HPLC).

         The disposition of ethoxyquin was similar when administered
    orally and intravenously. It was rapidly absorbed, with peak blood and
    tissue concentrations within 1 h. Excretion of the oral doses of 2.5
    and 25 mg/kg bw was extensive (> 85% within 24 h) and approximately
    1.5-fold greater via urine than faeces. The tissue concentrations at
    24 h were < 2% of the administered dose (Table 1). Little difference
    was seen with dose in rats, although the higher dose was excreted more
    slowly than the lower doses, attributed by the authors to delayed
    gastric emptying, and there was evidence of significant adipose
    deposition. The results after three or four repeated doses of 250
    mg/kg bw per day were reported to be similar to those after repeated
    and single dosing at 25 mg/kg bw, indicating induction of metabolizing
    enzymes and/or a return to normal gastric emptying (data not presented
    in the published report). The rate of excretion by mice was slightly
    more rapid than in rats. As parent ethoxyquin was not detectable in
    plasma at most times, the authors did not calculate its overall
    bioavailability. About 60% of the radiolabel in blood was in the
    plasma, and 8% was associated with precipitating plasma proteins.
    Repeated administration at 25 mg/kg bw per day and, to a lesser
    extent, 250 mg/kg bw per day to rats was followed by some evidence of
    bioaccumulation (data not presented) but not in muscle.


        Table 1. Tissue distribution at 24 h and excretion over 0-24 h as percent of 14C-ethoxyquin 
    administered orally or intravenously (i.v.)

                                                                                                          

    Species    Dose           Blood    Liver    Kidney    Muscle     Skin    Adipose    Urine    Faeces
               (mg/kg bw)                                                    tissue
                                                                                                          

    Rat        2.5 (oral)     0.7      1.4      0.3       0.4        0.3     0.9        57       31
               25 (oral)      1        1.3      0.2       0.7        0.4     1.7        64       26
               250 (oral)     0.9      1.6      0.2       1.8        1.2     12         41       11
               25 (i.v.)      1        1.5      0.2       1          0.7     6.4        57       23

    Mouse      2.5 (oral)     0.4      1.2      0.1       0.4        0.7     0.6        60       42
               250 (oral)     0.3      1        0.2       1.2        1.2     2.2        43       16
               25 (i.v.)      0.5      1.1      0.2       0.9        1.2     0.9        58       33
                                                                                                          

    From Sanders et al. (1996)
    Means of three to six animals
    

         After intravenous administration, the highest initial tissue
    concentrations were found in liver and kidney, although in mice a
    transiently high concentration was seen in adipose tissue at about 2 h
    (Table 2). A significant proportion (> 20%) of the intravenous dose
    was excreted in the faeces in both species (Table 1), and 40% of the
    administered dose was found in the bile of bile-cannulated rats,
    indicating that biliary excretion and enterohepatic circulation play a
    significant role in the toxicokinetics of ethoxyquin. Parent
    ethoxyquin was not detected in urine and was present in only trace
    amounts in faeces, liver, kidney, and adipose tissue. The elimination
    half-life in plasma for parent ethoxyquin was calculated to be 23 min
    (Sanders et al., 1996).

        Table 2. Tissue concentrations of 14C at different times after an intravenous 
    dose of 14C-ethoxyquin at 25 mg/kg bw as microgram equivalent per gram

                                                                                     

    Species      Time (h)     Blood    Liver    Kidney    Muscle    Skin     Adipose
                                                                             tissue
                                                                                     

    Rat          0.25         6        66       51        9         15       29 
                 2            5        27       21        2         10       29
                 12           2        12       11        < 1       3        24
                 24           3        9        10        < 1       1        15

    Mouse        0.25         10       45       40        11        27       40
                 2            4        27       17        3         16       67
                 12           2        9        8         < 1       3        22
                 24           2        5        3         < 1       2        2
                                                                                     

    From Sanders et al. (1996)
    Means for three animals
    
     (b)  Biotransformation

         Data summarized in the 1969 monograph (Annex 1, reference 13)
    indicate that the metabolism of ethoxyquin is extensive in rats, dogs,
    and chickens, although the metabolites were not identified. 

         Samples of urine, faeces, and tissues were obtained from rats and
    mice given [3-14C]ethoxyquin at 25 or 250 mg/kg bw orally or 25 mg/kg
    bw intravenously in the study of Sanders et al. (1996), described
    above. Urine and bile samples were stored frozen, defrosted, and
    centrifuged before separation by HPLC; liver, kidney, and faecal
    samples were extracted three times with 1:1:1 water:methanol:ethyl
    acetate, and the supernatants were separated by HPLC. Plasma samples
    were mixed 1:1 with acetonitrile prior to centrifugation and
    investigation by HPLC. The effects of incubation with glucuronidase

    containing arylsulfatase activity were also studied. Metabolites were
    investigated by HPLC, 1H-nuclear magnetic resonance spectroscopy, and
    three types of mass spectroscopy, including comparison with results
    for synthesized reference compounds.

         Eight metabolites were detected in urine, although only four were
    characterized (Table 3, Figure 1); no parent ethoxyquin was reported.
    The main metabolic pathway in both rats and mice seems to involve
     O-deethylation at C-6 followed by conjugation at C-6 with sulfate
    (metabolite G) or glucuronide (metabolite F). Subsidiary pathways of
    hydroxylation and glucuronidation at C-8 (metabolite H) or
     O-deethylation at C-6 and epoxidation between C-3,4 with sulfation
    at C-6 are also indicated. The major difference between rats and mice
    was the higher levels of glucuronidation in the latter. No significant
    difference was reported in the metabolite profiles of rats dosed with
    25 mg/kg bw orally or intravenously. Administration of ethoxyquin at
    250 mg/kg bw resulted in a greater proportion of radiolabel on the C-6
    sulfate (metabolite G) than after dosing with 25 mg/kg bw (Table 3).
    Six doses of 25 mg/kg bw resulted in a urinary metabolite profile
    similar to that after a single dose. Six doses of 250 mg/kg bw
    resulted in greater proportions of the glucuronide metabolites F and H
    and smaller proportions of metabolites G and E than after a single
    dose, indicating that sulfation may have been saturated or
    glucuronidation reactions induced. In the kidney and liver, the major
    metabolite was G. Faecal samples could not be satisfactorily extracted
    (< 30% recovery), and no reliable conclusions could be drawn. In the
    bile, three glutathione conjugates were detected, and < 5% of the
    radiolabel was present as the parent; this finding is cited as
    contrasting with the results of other workers, who had reported that
    most of the biliary radiolabel was present as ethoxyquin. The authors
    proposed a reaction scheme for the biliary metabolites (Figure 1)
    which involves production of reactive electrophilic intermediates
    (epoxides) (Burka et al., 1996).

     (c)  Effects on enzymes and other biochemical parameters

         Administration of ethoxyquin (purity unspecified) to male
    Sprague-Dawley rats at 5000 ppm in the diet for three days
    significantly induced both phase-1 and phase-2 xenobiotic metabolizing
    enzymes. Northern blotting of liver preparations for mRNA of
    cytochrome P450 (CYP) isozymes showed increasing amounts of CYP2B1 >
    2B2 > 3A2 > 1A2; assays for enzyme activity showed a twofold
    increase in the specific activity of CYP1A2 and a 10-fold increase in
    that of the CYP2B family. Blotting with probes for glutathione
     S-transferase mRNA showed that ethoxyquin increased Ya1, Ya2, and
    Yb1, with an approximate doubling of the activity of cytosolic
    glutathione  S-transferase. Enzyme assays and mRNA blotting also
    showed increases in NADPH-quinone oxidoreductase, gamma-
    glutamylcysteine synthetase, and UDP-glucuronosyl transferase
    activities. Ethoxyquin did not alter cellular glutathione
    concentrations or induce CYP1A1 (Buetler et al., 1995). 

    Table 3. Metabolic profile of 14C-ethoxyquin administered by oral 
    gavage to rats, as percent of total radioactivity in 24-h urine sample

                                                            

    Metabolitea     Dose (mg/kg bw)
                                                            
                    1  25    6  25    1  250    6  250
                                                            
    A               6         7         4          9
    B               6         5         4          7
    C               9         8         5          3
    D               7         6         2          < 1
    E               17        12        10         6
    F               5         6         3          15
    G               34        42        59         30
    H               3         4         4          14
    Parent          < 1       < 1       < 1        < 1
                                                            
    From Burka et al. (1996) 
    a See Figure 1 for structures


         Administration of diets containing ethoxyquin (purity
    unspecified) at 50, 100, 500, 2000, or 5000 ppm to male Sprague-Dawley
    rats for 14 days induced a range of effects on xenobiotic metabolizing
    systems. The liver:body weight ratios were increased at 5000 ppm: and
    total cytochromes P450 and b5 concentrations were increased by 30% at
    2000 and 5000 ppm. Analysis of the CO-reduced microsomal ultraviolet
    spectra showed that ethoxyquin-treated animals had a lambdamax of
    449.5 nm, indicating a phenobarbital-type induction pattern rather
    than a methylcholanthrene-type (lambdamax, 448 nm). Monooxygenase
    activity in microsomes from rats receiving ethoxyquin in the diet at
    5000 ppm was increased by 1.5 to 2-fold and epoxide hydratase activity
    by threefold when styrene oxide was the substrate, but the activities
    were slightly lower when benzo [a]pyrene was used as the substrate.
    Assays  in vitro with microsomes from animals induced with
    phenobarbital or methylcholanthrene showed that ethoxyquin inhibited
    arylhydrocarbon hydroxylase activity at concentrations of 5 mol/L and
    higher. Animals receiving both ethoxyquin-treated diet (5000 ppm) and
    methylcholanthrene (three intraperitoneal injections of 20 mg/kg bw)
    showed no evidence of additive induction of drug metabolizing systems.
    The NOAEL for changes in xenobiotic metabolizing enzyme systems was
    500 ppm, equivalent to 25 mg/kg bw per day (Kahl & Netter, 1977). 

    2.  Toxicological studies

     (a)  Acute toxicity

         Ethoxyquin had little acute toxicity, except when administered
    parenterally (Table 4). The clinical signs of toxicity after exposure
    to ethoxyquin were tremors, ataxia, hypoactivity, hypothermia, and

    FIGURE 1

        Table 4. Acute toxicity of ethoxyquin

                                                                                            

    Species    Route                    LD50 or LC50    Purity    Reference
                                        (mg/kg bw or    (%)
                                        mg/L air)
                                                                                            

    Rat        Oral gavage              1700            97.6      Varsho (1995a)
    Rat        Dermal (24 h)            > 2000          97.6      Varsho (1995b)
    Rat        Inhalation, whole body   > 2.0           97.6      Ulrich (1996)
    Mouse      Intraperitoneal          ~ 900                     Wilson & DeEds (1959)a
    Mouse      Intravenous              ~ 180                     Wilson & DeEds (1959)a
                                                                                            

    a Cited in 1969 JMPR monograph
    

    red-yellow staining of the fur. Gross and histopathological changes
    indicated an irritant effect on the gastrointestinal tract.

         Ethoxyquin produced transient, slight erythema when applied to
    rabbit skin for 4 h under semi-occlusive conditions. There was no
    oedema, but desquamation was present seven days after exposure
    (Varsho, 1995c). This result is consistent with the findings of a
    study summarized in the 1969 monograph (Kelly, 1960; cited in 1969
    JMPR monograph; Annex 1, reference 13).

         Ethoxyquin produced transient, slight-to-mild conjunctival
    redness and chemosis in rabbits. All of the effects had fully
    regressed within four days (Varsho, 1995d).

         In a sensitization study in six guinea-pigs of each sex,
    ethoxyquin was at most a very weak skin sensitizer. Induction was at
    100%, with challenge applications at 50% in acetone. Very weak
    erythematous responses were seen in both treated and control groups
    after challenge and re-challenge, one test animal producing a weak
    response to both challenge and re-challenge (Varsho, 1995e).

     (b)  Short-term studies of toxicity

     Rats

         Two studies of dietary administration of ethoxyquin to rats for
    200 days were summarized in the 1969 monograph. Kidney lesions
    (unspecified) were reported at 500 ppm and higher in males, with
    increased kidney:body weight ratios in males at 250 ppm and higher.
    The frequency of cytoplasmic inclusions in hepatocytes was increased
    at 2000 ppm (Wilson & DeEds, 1959; Cox, 1953; cited in 1969 JMPR
    monograph; Annex 1, reference 13).

         In a study described in more detail below of the effects of
    ethoxyquin on induction of liver tumours by  N-nitrosodiethylamine, a
    control group received ethoxyquin only. Thus, 15 male Fischer 344
    rats, six weeks old, received an intraperiotneal injection of 0.9%
    saline, were placed on a diet containing 8000 ppm ethoxyquin (purity
    unspecified), equivalent to 500 mg/kg bw per day in young rats, in
    week 2, and were partially (66%) hepatectomized in week 3. When the
    animals were killed at week 8, a background level of gamma-glutamyl
    transpeptidase (gamma-GT)-positive foci was found in the liver (Ito et
    al., 1985).

         Groups of five male and five female Sprague-Dawley rats received
    ethoxyquin (purity, 97.6%) by gavage in corn oil for 28 days at doses
    of 0, 50, 250, 500, or 1000 mg/kg bw per day. Histopathological
    examination was limited to the liver, lung, kidney, stomach, and gross
    lesions in animals at 50, 250, and 1000 mg/kg bw per day. All of the
    animals at 1000 mg/kg bw per day had died by day 3 with multiple organ
    involvement; the cause of death in two animals was considered to be
    necrosis and ulceration of the forestomach. The prevalences of
    salivation, stained fur, and brown urine were increased at 250 mg/kg
    bw per day and higher. Initial body-weight gain was reduced by 50% in
    males receiving 500 mg/kg bw per day. Erythrocyte count, haematocrit,
    and haemoglobin concentration were decreased by about 10% in females
    at 250 mg/kg bw per day and in animals of each sex at 500 mg/kg bw per
    day. Alterations in serum clinical chemical parameters were seen in
    both males and females, but were more frequent in males at 250 and
    500 mg/kg bw per day; they included increased quantities of protein,
    total bilirubin, cholesterol, inorganic phosphorus, potassium, and
    calcium, and gamma-GT activity, while the concentration of glucose was
    decreased. Increased absolute and relative liver weights (>  40%)
    were seen in animals of each sex at 250 mg/kg bw per day and higher,
    and the relative kidney weights were increased (< 10%) in a
    dose-related fashion. There were no gross lesions at doses < 1000
    mg/kg bw per day. Histopathological investigation showed kidney
    lesions (interstitial infiltration, tubular epithelial regeneration,
    and tubular dilatation) in males receiving 50 and 250 mg/kg bw per day
    and in animals of each sex at 500 mg/kg bw per day. The incidences of
    haemorrhage and oedema of the lung and hepatocellular swelling were
    increased at 500 mg/kg bw per day. A NOAEL was not identified (Naas,
    1997).

         Groups of 10 Sprague-Dawley rats of each sex, six weeks old at
    the beginning of the study, received ethoxyquin (purity, 97.6%) by
    gavage in corn oil at 0, 20, 40, 200, or 400 mg/kg bw per day for 13
    weeks. Minor overdosing (2-14%) of the group at 200 mg/kg bw per day
    on day 67 is considered not to have compromised the study.
    Ophthalmoscopy was performed before treatment and during week 12. A
    full post-mortem examination was performed on all animals, and samples
    of lung, liver, kidney, and gross lesions from all animals were
    examined histologically, as were more than 30 tissues from controls
    and from animals at the highest dose. 

         There were no deaths during the study. Clinical signs were seen
    in animals of each sex, but more often in females, at 200 and 400
    mg/kg bw per day, including staining of various body parts and
    particularly the anogenital area, salivation, and brown urine.
    Body-weight gain was clearly reduced in males at 200 and 400 mg/kg bw
    per day, with a slight effect (10%) at 40 mg/kg bw per day; food
    consumption was similar in test and control groups. Haematological and
    clinical chemical parameters were altered in animals of each sex at
    400 mg/kg bw per day, and many were also significant at 200 mg/kg bw
    per day. These included increased reticulocyte counts, total
    bilirubin, blood urea nitrogen, gamma-GT activity, cholesterol, and
    thyroid-stimulating hormone; and decreased erythrocyte and leukocyte
    counts, prothrombin time, and glucose. Urine was more deeply coloured
    at 200 and 400 mg/kg bw per day, and the volume was increased in
    animals at the highest dose, with no change in specific gravity. There
    were no treatment-related effects on the eyes. 

         The main gross finding was reddened thyroids in animals of each
    sex at 200 and 400 mg/kg bw per day. The absolute weights of the liver
    and that relative to body weight were increased in a dose-related
    fashion (by 15-70%), and those of the kidneys increased by 4-20% in
    animals of each sex at 200 and 400 mg/kg bw per day; changes in the
    body-weight ratios of brain and testes are considered to be secondary
    to the reduced body weights. Histological examination identified the
    kidney as the main target organ in animals of each sex, with increased
    incidences of tubular mineralization, papillary necrosis, and
    cytoplasmic vacuolation in males at the high dose; and increased
    incidences of mineralization, papillary necrosis, and nephropathy in
    females at the high dose. The incidence of nephropathy was also
    increased in females at 200 mg/kg bw per day. The incidence of
    ultimobranchial cysts of the thyroid was increased in males receiving
    200 and 400 mg/kg bw per day and females receiving 200 mg/kg bw per
    day. Increased incidences of cytoplasmic vacuolation of the adrenals,
    suppurative inflammation of the epididymides, non-suppurative
    inflammation of the prostrate, mineralization of the lung, and
    alveolar histiocytosis were also seen in males at the high dose, and
    the incidences of inflammation of the oesophagus and epithelial
    hyperplasia of the thymus were increased in females at this dose. It
    should be noted that only gross lesions, liver, lung, and kidney were
    examined from groups at lower doses. As the decrease in body-weight
    gain in males at 40 mg/kg bw per day was part of a dose-response
    relationship and was not associated with reduced food consumption, the
    NOAEL for this study was 20 mg/kg bw per day (Naas, 1996a).

     Dogs

         A one-year study in three dogs given ethoxyquin by gavage was
    summarized in the 1969 monograph; the NOAEL was 3 mg/kg bw per day.
    The effects reported at the next highest dose (10 mg/kg bw per day)
    included renal nephrosis, increased bromosulphthalein retention
    indicating liver dysfunction, and abdominal tenderness (Hanzal, 1955;
    cited in 1969 JMPR monograph; Annex 1, reference 13).

         Groups of one male and one female beagles received ethoxyquin
    (purity, 97.6%) by capsule at a dose of 0, 25, 50, 100, or 200 mg/kg
    bw per day for 28 days. All of the animals at 100 or 200 mg/kg bw per
    day group died or were sacrificed by day 17 or day 7, respectively;
    one female at 50 mg/kg bw per day was sacrificed on day 21. The signs
    seen in dogs that died and in survivors included hypoactivity, reduced
    defaecation, brown urine, and pale gums. Given the small initial group
    sizes and the deaths, only major, consistent changes are summarized
    here. Reduced body-weight gain and food consumption were seen at all
    doses. The serum activities of enzymes indicative of liver damage were
    increased at four weeks in all groups in which they were measured (25
    and 50 mg/kg bw per day): alkaline phosphatase by fivefold, aspartate
    aminotransferase by threefold, alanine aminotransferase by 20-fold,
    and gamma-GT by threefold; there were indications of reduced activated
    partial thromboplastin times. The ratios of liver and kidney weights
    to body weight were increased at 25 and 50 mg/kg bw per day. Common
    post-mortem findings included redness of the gastrointestinal tract
    and darkened livers. Histological examination showed pigmentation of
    the liver in all treated animals but not in controls. A NOAEL was not
    identified (Naas, 1996b).

         In a 90-day study, groups of five beagles of each sex were given
    ethoxyquin (purity, 97.6%) by capsule at 0, 2, 4, 20, or 40 mg/kg bw
    per day. Clear signs of toxicity were seen during the first seven
    weeks of the study at 40 mg/kg bw per day, including reduced body
    weight, staining of the body surface, brown urine, brown sclera, dark
    mucoid faeces, and emesis, and these groups received only empty
    capsules for the final six weeks of the study, effectively becoming
    reversibility groups. Investigations of clinical chemistry (including
    thyroid hormones), haematology, and ophthalmoscopy were performed
    before treatment and at weeks 4 and 12 or 13. Post-mortem
    investigations included microscopic examination of a wide range of
    tissues from all animals and special stains for pigment
    identification. 

         One female at the highest dose was sacrificed  in extremis on
    day 13. Other findings were similar in males and females. Clinical
    signs including brown staining of the abdomen and urogenital area,
    brown urine, decreased faeces, and emesis were seen regularly at 20
    and 40 mg/kg bw per day and occasionally during the 4 h after dosing
    at 4 mg/kg bw per day; these signs were still present between weeks 7
    and 13 ('recovery') in animals at the highest dose. Body-weight loss
    occurred at 40 mg/kg bw per day in weeks 1-7, which reversed when
    dosing stopped, but females had a lower (12%) mean body weight than
    controls at termination. At 20 mg/kg bw per day, body-weight gain was
    reduced (60%) throughout the study. Food consumption was reduced at 20
    (20%) and 40 mg/kg bw per day (up to 50%). The only notable change in
    haematological parameters was a dose-related decrease in activated
    partial thromboplastin times in males at 4 mg/kg bw per day and higher
    and in females at the highest dose. Marked increases in total
    bilirubin concentration and in alkaline phosphatase, alanine
    aminotransferase, aspartate aminotransferase, and gamma-GT activities
    in serum, indicative of liver dysfunction, were seen at 20 mg/kg bw

    per day in weeks 4 and 12 or 13 and at 40 mg/kg bw per day in week 4
    only; alanine aminotransferase and, to a lesser extent, alkaline
    phosphatase activities were also increased at 4 mg/kg bw per day. By
    week 13, the serum values in animals at 40 mg/kg bw per day
    (seven-week treatment, six-week recovery) had returned approximately
    to control values. There were no significant changes in absolute or
    relative organ weights. Treatment-related gross and microscopic
    findings were limited to the liver. At 20 and 40 mg/kg bw per day, a
    darkened appearance was associated microscopically with increased
    pigment deposition, hepatocellular necrosis, cytoplasmic vacuolation,
    and bile-duct hyperplasia; at 4 mg/kg bw per day, occasional findings
    of mild or moderate pigmentation, minimal hepatocellular necrosis, and
    vacuolation were recorded. The pigments were found to be porphyrin and
    bilirubin in most cases, some sections also staining for haemosiderin.
    The NOAEL was 2 mg/kg bw per day (Naas, 1996c).

     (c)  Long-term studies of toxicity and carcinogenicity

     Mice

         Solutions of ethoxyquin (as Santoquin(R)) at 10 or 50 mg/ml
    were administered subcutaneously to neonatal Swiss ICR/Ha mice on days
    1 and 7 (0.1 ml) and 14 and 21 (0.2 ml) of age or as a single dose of
    100 mg/ml (0.1 ml on day 1). Each dose was equal to 500, 2500, and
    5000 mg/kg bw on day 1 and 250 and 1250 mg/kg bw on day 21. The groups
    consisted of 57 mice at the low dose, 53 at the intermediate dose, and
    28 at the high dose. By the time the mice were weaned, 100% at the
    high dose, 74% at the intermediate dose, and 2% at the low dose had
    died; 15% of controls had died at this time. Small groups of mice were
    sacrificed at various times up to termination at week 53. A limited
    range of tissues and lesions were examined primarily for tumours. The
    incidences of pulmonary tumours and hepatomas were similar in the
    treated and control groups; a slight increase in the incidence of
    malignant lymphoma in four females at the low dose and two at the
    intermediate dose, with none in controls, was considered equivocal by
    the authors. The results indicates that four subcutaneous
    administrations of ethoxyquin at near-lethal doses to neonatal mice
    did not significantly increase the incidence of tumours in mice up to
    one year of age (Epstein et al., 1970).

     Rats

         A two-year study of ethoxyquin in the diet of rats was summarized
    in the 1969 monograph. Groups of approximately 10 male and 10 female
    rats were fed diets containing ethoxyquin at concentrations of 0, 62,
    125, 250, 500, 1000, 2000, or 4000 ppm for up to two years. The
    animals were sacrificed for autopsy after 200, 400, 600, or 715 days.
    The mortality rates were not significantly different from those of
    controls. Significantly reduced body-weight gain was seen at 2000 ppm
    after 225 days in males and after 21 days in females. After 200 days,
    increased relative liver and kidney weights were found in males at 250
    ppm and in females at 1000 ppm. The haemoglobin values for animals of
    each sex were normal 100 and 300 days after the start of the

    experiment in rats fed 2000 and 4000 ppm. Histological changes in the
    renal cortex were clearly evident after 200 days in male rats
    receiving 2000 or 4000 ppm but not in females. All other organs were
    normal in animals of each sex after 200 days. After 400 days, lesions
    in the kidneys (pyelonephritis), liver, and thyroid were seen in males
    only. Similar lesions were seen for periods up to 717 days in animals
    of each sex, although they were more marked in males. Occasional
    tumours were found after 700 days, but the incidence was unrelated to
    dose, and they were also seen in controls. No clearly defined effects
    were evident after feeding 62 ppm, but minute lesions were present in
    the kidneys of two males receiving 500 ppm. It was difficult to
    distinguish the abnormalities in the group examined after 700 days
    from the pathological manifestations of senility after that time
    (Wilson & DeEds, 1959; cited in 1969 JMPR monograph; Annex 1,
    reference 13). The 1969 JMPR concluded that the NOAEL was 125 ppm,
    equivalent to 6 mg/kg bw per day. The small groups used in this study
    limit its sensitivity for detecting changes in rare events such as
    tumours with low background rates; however, the wide spread of doses
    and sequential sampling times provides a degree of assurance in the
    reported findings.

         As part of an investigation of kidney and liver tumours induced
    by  N-nitrosoethyl- N-hydroxyethylamine, one control group received
    only ethoxyquin. This group of 25 male Fischer 344 rats received a
    diet containing 8000 ppm ethoxyquin from nine weeks of age to
    termination at 41 weeks of age. Sections of liver, kidney, and gross
    lesions were investigated histologically. No gamma-GT-positive foci,
    hyperplastic nodules, or hepatocellular carcinoma were found in the
    liver; no data were presented on kidney lesions. A control group of 25
    male Fischer 344 rats received a diet containing 8000 ppm ethoxyquin
    as part of a parallel investigation of urinary bladder carcinogenesis
    induced by  N-nitrosobutyl- N-hydroxybutylamine. After 32 weeks,
    there were higher incidences of simple hyperplasia and papillary or
    nodular hyperplasia of the urinary bladder than in groups receiving
    ascorbic acid or sodium erythorbate, the incidence of simple
    hyperplasia being greater than that induced by
     N-nitrosobutyl- N-hydroxybutylamine alone; no untreated controls
    were used. No urinary bladder papillomas or carcinomas were seen in
    the group receiving ethoxyquin only (Ito et al., 1985).

         An almost identical study of urinary bladder carcinogenesis
    showed that 24 weeks' exposure to a diet containing 8000 ppm
    ethoxyquin, considered to be equivalent to 400 mg/kg bw per day, did
    not induce papillary or nodal hyperplasia or papilloma of the urinary
    bladder in a group of 15 male Fischer 344 rats (Miyata et al., 1985).

         The dependence of the renal lesions produced by ethoxyquin on age
    and sex was investigated in Fischer 344 rats. Groups of four to eight
    male rats received diets containing ethoxyquin (purity, 90%) at 5000
    ppm from three or eight weeks of age for 20, 26, or 30 weeks. Eight
    female rats received a diet containing 5000 ppm ethoxyquin for 30
    weeks from eight weeks of age. Histopathological examination of the
    kidney comprised bromodeoxyuridine (BrdU) labelling, gamma-GT

    histochemistry, haematoxylin and eosin staining, Alizarin red
    staining, and immunoblotting of urine samples for albumin and alpha2u
    globulin. Body-weight gain was reduced by 10-15% in treated animals.
    In males, the absolute kidney weights were increased by 5-50%, with a
    consequent increase in the relative weights; females showed a 12%
    increase in kidney:body weight ratios. Renal cortical changes were
    seen in all treated males, consisting of eosinic cytoplasmic
    inclusions in tubular epithelial cells and protein accumulation in the
    lamina of the tubules. In males dosed from three weeks of age,
    papillary necrosis, slight calcium deposition, and hyperplasia of the
    transitional epithelium of the renal pelvis were seen. The
    histological appearance of the kidneys of treated females was similar
    to that of controls, except for high concentrations of lipofuscin
    deposition. BrdU labelling was increased in males at 30 weeks, but not
    at 20 weeks, in both regenerating basophilic tubules and those
    staining normally with haematoxylin and eosin; BrdU labelling in
    females was not described. The concentrations of alpha2u globulin in
    urine were slightly lower in treated males, but those of albumin were
    significantly increased. The time of first exposure can thus
    significantly alter the pattern of renal lesions in rats consuming
    diets containing ethoxyquin at 5000 ppm, equivalent to 250 mg/kg bw
    per day, exposure from three weeks of age resulting in papillary
    necrosis in addition to the cortical lesions seen in animals exposed
    from eight weeks of age (Manson et al., 1992).

         Groups of 6-19 Fischer 344 rats of each sex, three weeks of age
    at the start of the study, received diets containing ethoxyquin
    (purity unspecified) at 0 or 5000 ppm for up to 18 months; one group
    received ethoxyquin in the diet for 24 weeks followed by 34 weeks on
    control diet. The study was designed to investigate the progression of
    renal lesions and involved interim sacrifices at 4, 12 or 14, 24, 58,
    and 78 weeks. The body-weight gain of treated females was reduced in
    weeks 1-5 and that of males from week 3 onwards; food consumption was
    reduced in animals of each sex during the first four weeks.
    Investigations of renal pathology showed a clear difference between
    males and females. Males had significant interstitial degeneration of
    the papilla at weeks 4 and 14, which progressed to necrosis with
    pyelonephritis of the cortex and urothelial hyperplasia of the renal
    pelvis by week 24. In females, interstitial degeneration of the
    papilla was only slight at week 14 and did not progress consistently.
    The chronic progressive nephropathy commonly seen in Fischer 344 rats
    was accelerated in animals receiving ethoxyquin. The authors reported
    that this was more marked in males, but the data presented do not
    substantiate that statement. A golden-brown pigmentation, found to be
    lipofuscin by Schmorl's stain, was noted in the proximal tubules of
    treated rats, particularly females. The lesions present at 24 weeks
    showed no evidence of reversibility after 34 weeks on control diets.
    The authors considered that there was no evidence for preneoplastic
    proliferative lesions. This study showed that ethoxyquin at 5000 ppm
    in the diet, equivalent to 250 mg/kg bw per day, is a potent
    nephrotoxin in young male Fischer 344 rats (Hard & Neal, 1992). 

         A number of reports have been published of the results of
    investigations into the effects of antioxidants, including ethoxyquin,
    on the induction of neoplasia and preneoplastic lesions by known
    carcinogens. The most comprehensive series of studies with ethoxyquin
    is probably that of Ito and co-workers (Ito et al., 1985; Miyata et
    al., 1985; Masui et al., 1986), who used Fischer 344 rats to
    investigate moderation of effects on the liver induced by
     N-nitrosodiethylamine, effects on the kidney and liver produced by
     N-nitrosoethyl- N-hydroxyethylamine, and effects on the bladder
    produced by  N-nitrosobutyl- N-(4-hydroxybutyl)amine.

         Groups of 18 six-week-old male Fischer 344 rats received an
    intraperitoneal injection of 200 mg/kg bw  N-nitrosodiethylamine in
    0.9% saline; two weeks later, they were transferred to a diet
    containing 0 or 8000 ppm ethoxyquin (purity unspecified) and underwent
    a partial (60%) hepatectomy one week later. The rats were sacrificed
    at week 8, and liver sections were stained with haematoxylin and eosin
    and a histochemical stain for gamma-GT-positive foci. The rats
    receiving ethoxyquin had a significant  (p < 0.001) decrease in the
    number of foci (0.9 versus 3.3/cm2) and in the area of the foci (0.06
    versus 0.19 mm2/cm2) (Ito et al., 1985). 

         Groups of 23 or 27 six-week-old male Fischer 344 rats received
    drinking-water containing 0.1%  N-nitrosoethyl- N-hydroxyethylamine
    for two weeks; between weeks 3 and sacrifice at week 32, they received
    diets containing 0 or 8000 ppm ethoxyquin (purity unspecified). All
    rats had gamma-GT-positive foci, but the ethoxyquin-treated group had
    fewer (1 versus 21/cm2) and smaller (10 versus 22 mm2/cm2) foci.
    The group given ethoxyquin also had a reduced area of hyperplastic
    nodules (2.3 versus 7 mm2/cm2), and fewer animals had hepatocellular
    carcinomas (3/27 versus 11/23). Conversely, the kidneys of the
    ethoxyquin-treated group had higher frequencies of atypical-cell foci
    (0.9 versus 0.2/cm2) and adenomas (5.6 versus 0.8/cm2), and there
    were more animals with foci (26/27 versus 12/23) and adenomas (17/27
    versus 5/23) and larger foci (5.6 versus 0.9  10-2 mm2/cm2) and
    adenomas (24 versus 8  10-2 mm2/cm2) (Ito et al., 1985). 

         Groups of 25 six-week-old male Fischer 344 rats received
    drinking-water containing 0.05%
     N-nitrosobutyl- N-(4-hydroxybutyl)amine for four weeks; between
    weeks 4 and sacrifice at week 36, they received diets containing 0 or
    8000 ppm ethoxyquin (purity unspecified). Examination of the urinary
    bladders showed that ethoxyquin had increased the incidence of animals
    with simple hyperplasia (25/25 versus 14/24), the incidence and extent
    of papillary or nodular hyperplasia (25/25 versus 8/24 and 9.4 versus
    0.48/10 cm of basement membrane), the incidence and extent of
    papillomas (17/25 versus 5/24 and 1.1 versus 0.19/10 cm), and the
    incidence and extent of carcinomas (4/25 versus 1/24 and 0.17 versus
    0.04/10 cm) (Ito et al., 1985). A similar study involving two weeks'
    dosing with  N-nitrosobutyl- N-(4-hydroxybutyl)amine (0.05% in
    water) and sacrifice at 24 weeks also showed that dietary
    administration of ethoxyquin at 8000 ppm (purity unspecified)

    increased the incidence and extent of papillary or nodular hyperplasia
    but not of papillomas of the urinary bladder (Miyata et al., 1985).

         This group of studies shows that ethoxyquin markedly reduces the
    preneoplastic effects of  N-nitrosodiethylamine and
     N-nitrosoethyl- N-hydroxyethylamine on the liver, possibly by a
    combination of antioxidant effects and induction of detoxification
    mechanisms. The increase produced by ethoxyquin in the incidence of
    neoplastic and preneoplastic kidney lesions induced by
     N-nitrosoethyl- N-hydroxyethylamine may be secondary to the direct
    toxic effects of ethoxyquin on the kidney. The mechanism of the
    effects of ethoxyquin on
     N-nitrosobutyl- N-(4-hydroxy-butyl)amine-induced urinary bladder
    neoplasia is unknown. 

     Dogs

         Ethoxyquin was fed to two groups of 14 dogs and bitches at a
    dietary concentration of 0 or 300 ppm for five years. No effects were
    observed on haematological, urinary, or clinical chemical end-points
    (aspartate aminotransferase activity, blood urea nitrogen, and
    bromosulphthalein retention), organ weights, organ:body weight ratios,
    body weight, or gross or histopathological appearance (Monsanto, 1966;
    cited in 1969 JMPR monograph; Annex 1, reference 13). The 1969 JMPR
    concluded that the NOAEL in this study was 300 ppm, equivalent to 7.5
    mg/kg bw per day.

     (d)  Genotoxicity

         A number of published papers indicate that ethoxyquin is not
    genotoxic in bacterial systems (Table 5); however, these reports could
    not be validated as only minimal details were available. The results
    of assays in eukaryotic systems have not been reported. 

     (e)  Reproductive toxicity

    (i)   Multigeneration reproductive toxicity

     Rats

         After 40 days on a diet slightly deficient in tocopherol and
    containing 0, 250, 500, or 1000 ppm ethoxyquin, rats were bred to
    produce three consecutive litters. The offspring of the first litter
    were used to produce a second-generation litter. The highest dose was
    discarded after production of one litter (reason unknown). No effects
    on reproduction, as reflected in fertility, litter size, or survival
    of offspring, were observed. The animals receiving the experimental
    diet produced young and raised them more successfully than controls,
    the 500 ppm diet being more effective than the 250 ppm diet (Wilson,
    1956; Wilson & DeEds, 1959, cited in 1969 JMPR monograph; Annex 1,
    reference 13). The short dosing period before mating and the unknown
    purity and group size compromise this report to some extent, but it


        Table 5. Results of assays for the genotoxicity of ethoxuquin

                                                                                                               

    End-point            Test system          Concentration         Purity    Result       Reference
                                                                    (%)
                                                                                                               

    Reverse mutation     S. typhimurium       10-1000 g/plate      'Pure'    Negativea    Joner (1977)
                         TA98, TA100,
                         TA1535, TA1537,
                         TA1538

    Reverse mutation     S. typhimurium       > 5000 g/plate       NR        Negativea    Ohta et al. (1980)
                         TA98, TA100, 
                         TA1535, TA1537, 
                         TA1538; E. coli 
                         WP2 hcr trp

    Reverse mutation     NR                   NR                    NR        Negative     Zeiger (1993)

    Gene mutation        B. subtitlis H17     0.2 ml                NR        Negative     Ohta et al. (1980)
                         rec+ and M45 rec-
                                                                                                               

    a  With and without metabolic activation
    

    can be concluded that ethoxyquin in the diet at 500 ppm, equivalent to
    25 mg/kg bw per day, has no marked effect on reproductive outcome.

         Another study cited in the 1969 JMPR monograph had some results
    contrary to those described above. Groups of eight or nine female rats
    were placed on diets containing 0, 125, 375, or 1125 ppm ethoxyquin on
    the day of mating. The length of gestation was comparable in all
    groups, but the litter size was slightly depressed at doses of 375 ppm
    and higher, and at 1125 ppm the incidence of stillbirths was increased
    and survival to weaning was decreased. The NOAEL in this unusual study
    was 125 ppm, equivalent to 6 mg/kg bw per day. In a separate part of
    the same study, no effects were found on litter size, the number of
    stillbirths, survival to weaning, or weanling weight in rats receiving
    up to 1125 ppm ethoxyquin in the diet starting between days 1 and 10
    of gestation (Derse, 1956; cited in 1969 JMPR monograph; Annex 1,
    reference 13).

     Dogs

         The effects of ethoxyquin on reproduction over two generations
    were studied in groups of beagles. Dogs were chosen as ethoxyquin is
    added to commercial dog food to help prevent oxidative deterioration.
    In the first mating (F0), groups of five males and 10 females
    received diets containing ethoxyquin (Santoquin(R)) at a mean
    analytical concentration of 0, 100, or 225 ppm for a minimum of 82
    days before pairing. The eight male and 13 female pups used
    subsequently for the F1 matings received diets containing 0, 100, or
    225 ppm ethoxyquin from weaning until breeding at 10-30 months (2nd
    estrus cycle in females). Semen samples were taken during the first
    week of treatment and at around the time of breeding in order to
    determine the volume, sperm count, motility, speed, and morphology.
    Animals were observed and underwent extensive physical examinations
    routinely; if possible, they were also observed during labour. Mating,
    whelping, and lactation indices were determined. Urine samples and
    blood samples were taken for haematology and clinical chemistry from
    fasted adults before treatment and at the end of the F0 phase; at
    weeks 10, 23, 36, 49, and 62 and at termination in the F1 growth
    phase; and at termination of the F1 mating phase. Ophthalmological
    examinations were performed at the beginning and end of the F1 growth
    and mating phases. All F1 adults and pups that showed signs of
    toxicity were necropsied. A range of tissues from controls and F1
    adults at the high dose were examined histologically, with selected
    tissues from F2 pups that showed clinical signs; the livers and
    gall-bladders from F1 adults at the low dose and the adrenals and
    spleens from F1 adult females at the low dose were also examined.
    Macroscopic and microscopic examinations were performed only on F0
    and F1 animals that died or were sacrificed prematurely.

         In the F0 mating, there was considerable intra-group variation
    in body weights, but F0 adults receiving 225 ppm ethoxyquin showed a
    trend for reduced body weight from the initiation of dosing to week 17
    and during the latter stages of gestation. Males thad reduced food

    consumption during most of the study. Two females at the high dose
    that were confirmed to be pregnant did not give birth. There were no
    other differences between the groups in mating performance, labour,
    birth, or weaning indices, semen parameters, or clinical signs. Litter
    size, pup survival, and pup weight and growth were similar in all
    groups. At 225 ppm, there was an increased number of pups of each sex
    with a raw or red anus, dehydration, nasal discharge, and excessive
    lachrymation; the incidence of the last two signs was also increased
    at 100 ppm. Statistically significant increases in serum alkaline
    phosphatase activity were seen in male parents at the high dose and in
    female parents at the low and high dose; there was also an indication
    of reductions in monocytes and partial thromboplastin times in animals
    of each sex at the high dose, although all of the values were claimed
    to be within the normal ranges. There were no effects on urinary
    parameters. Remating of three female controls and two at 225 ppm from
    this phase which failed to mate during the initial phase was
    successful.

         Among F1 animals, one male at the low dose and two females at
    the high dose died or were sacrificed  in extremis. The male was
    sacrificed because of suspected neurological signs; one of the females
    died of suspected heart disease, and the other was sacrificed because
    of pneumonia. The clinical signs included excessive lachrymation,
    dehydration, thinness, and pale gums and showed a dose-related
    increase in both the number of animals of each sex with a particular
    sign and the number of occasions on which it was observed. Males at
    the high dose had a lower mean body weight than controls up to week 48
    of the study. Initially, animals at the high dose consumed more food
    than controls, but food consumption was consistently lower in weeks
    8-18 in males and in weeks 8-30 in females. Considerable variations in
    haematological end-points were seen throughout the study in both
    treated and control animals. There was evidence of treatment-related
    effects on erythrocyte count, haematocrit, and haemoglobin, which were
    reduced by up to 11% relative to controls in treated males and females
    at weeks 10 and 23, and on partial thromboplastin times, which were
    reduced in females at the high dose in weeks 23 and 36 and in females
    at the low dose in weeks 23 and 62 and at the final analysis.
    Increased serum activities of alkaline phosphatase, gamma-GT, and
    alanine aminotransferase and reduced albumin:globulin ratios were
    found in animals at the high dose in weeks 10, 23, and 36, with
    evidence of lesser perturbations at the lower dose. These changes are
    indicative of impaired liver function. The results of urinary analysis
    were unremarkable.

         In the F1 mating, there were no clear differences in semen
    analyses or mating, gestation, whelping, or weaning indices between
    control and ethoxyquin-treated animals. In adults, the only
    treatment-related clinical sign was excessive lachrymation, which
    occurred more frequently in males at the low and high doses than in
    controls. Haematological end-points were similar in all groups.
    Dose-related changes were seen in a number of clinical chemical
    parameters in females, which attained statistical significance
     (p < 0.05) at the high dose. These comprised reductions in glucose,

    cholesterol, protein, albumin, and albumin:globulin ratio, and
    increases in total bilirubin concentration and in gamma-GT, alkaline
    phosphatase, and alanine aminotransferase activities. In males, the
    dose-related increases in alkaline phosphatase, gamma-GT, and alanine
    aminotransferase activities did not attain statistical significance.
    Macroscopic examination showed dark-plum-coloured livers in one male
    and two females at the high dose and cervical lymph node haemorrhages
    in two females at the low and high doses; these lesions were possibly
    related to treatment as they were not present in control animals.
    Increases in the absolute weights of the spleen and testes and in the
    weights of these organs relative to the brain weight were seen in
    treated males, giving statistically significant increases in relation
    to body weight. In females, increases in the absolute and relative
    weights of the liver (10%), kidneys (10%), and spleen (40%) were
    reported but were not statistically significant. Histopathological
    examination showed that the liver, pituitary, and spleen were the
    target organs. The macroscopic finding of increased cervical lymph
    node haemorrhage in females was not confirmed. A dark-reddish-brown
    pigment, subsequently identified as protoporphyrin IX, was not found
    in the livers of controls or males at the low dose but was present in
    the livers of 7/13 females at the low dose, 2/7 males at the high
    dose, and 10/11 females at the high dose, with a dose-related increase
    in severity. The frequencies of fibrosis and haemorrhage of the spleen
    were increased in females at the high dose (3/11 versus 0/13 in
    controls), and the incidence of pituitary cysts was increased in
    animals at the high dose when compared with controls (2/6 versus 0/8
    in males and 4/10 versus 2/12 in females) 

         Treated male pups had increased incidences of grey or pale gums,
    excessive lachrymation, and dehydration, and female pups had an
    increased incidence of dehydration. The pup weights at birth and to
    week 6 of gestation were slightly reduced (< 10%), with a
    dose-related effect in female pups. An increased mortality rate in
    pups at the low dose was not seen at the high dose and was probably
    related to the larger litter sizes in this group; the rates of
    mortality were 7/62 controls, 24/91 at the low dose, and 10/77 at the
    high dose.

         During the study, four males and one female at 100 ppm and two
    females at 225 ppm showed signs of neuropathy: The animals had
    impaired hindlimb function, inability to stand, and unsteadiness of
    the head and body which was found to be associated with myelin
    degeneration. Examination of clinically normal littermates showed no
    neurological deficits. The breeding records showed that all of the
    affected animals had a common male ancestor which was not in the
    breeding line of any of the control animals. When the parents of some
    of the affected pups were removed from the treated diets and mated,
    the incidence of neurologically affected animals was 17% in one litter
    and 25% in the other. The evidence from this part of the study is
    strongly indicative of a genetic etiology.

         Estimation of the actual intakes of ethoxyquin in this study was
    confounded by up to twofold increased consumption during lactation and
    the fact that 180 and 360 ppm had to be added to obtain nominal
    concentrations of 150 and 300 ppm, however, the analysis showed mean
    initial values of 100 and 225 ppm. Although the actual amounts of food
    consumed varied during the study, a value of 25 g/kg bw per day was
    considered to be a representative mean, which resulted in intakes of
    2.5 mg/kg bw per day ethxyquin at 100 ppm and 6 mg/kg bw per day at
    225 ppm.

         The results of this study show that ethoxyquin in the diet at
    concentrations up to 225 ppm did not affect reproductive performance
    or outcome in beagles. There was no clear overall NOAEL because of
    increased incidences of clinical signs such as excess lachrymation and
    dehydration, clinical chemical changes and pigment deposition in the
    liver. The lowest dose, 100 ppm, equal to 2.5 mg/kg bw per day, was
    considered to be the minimal effect level (Gilman & Voss, 1995).

     (ii)  Developmental toxicity

     Rats

         In a range-finding study for teratogenicity in Sprague-Dawley
    rats, groups of eight mated females received ethoxyquin (purity,
    97.6%) by gavage in corn oil at 0, 62, 125, 250, 500, or 1000 mg/kg bw
    per day on days 6-19 of gestation. All animals given 1000 mg/kg bw per
    day died or were sacrificed by day 9, and three animals given 500
    mg/kg bw per day died between days 10 and 11 of gestation; post-mortem
    examinations did not show any adverse effects. Clinical signs of
    reduced defaecation, dark urine, and brown staining of fur were
    dose-related and affected all treated groups. Reduced food consumption
    and body-weight loss were seen at doses > 125 mg/kgbw per day at
    the beginning of dosing; from day 9 onwards, body-weight gain was
    similar in all groups up to 500 mg/kg bw per day, and these animals
    had a 20% body-weight deficit by day 20 when compared with controls.
    Fetal weights were reduced at 500 mg/kg bw per day, but examination
    for external malformations, sex ratio, and crown-rump length showed no
    effects of treatment (Nemec, 1996a).

         In the main study, groups of 25 mated female Sprague-Dawley rats
    received ethoxyquin (purity, 97.6%) by gavage in corn oil at 0, 50,
    150 or 350 mg/kg bw per day on days 6-19 of gestation. The dams were
    sacrificed on day 20, their uteri and ovaries were examined, and all
    fetuses were investigated for weight, sex, and external and visceral
    malformations. The heads of one-half of the fetuses were examined by
    Wilson sectioning and the other half by mid-coronal section. All
    fetuses were stained with Alizarin Red S for skeletal investigation.
    There were no deaths during the study. Urogenital staining was seen in
    dams after treatment at the highest dose, and staining of other areas
    was also seen in these and in some animals receiving 150 mg/kg bw per
    day. At 350 mg/kg bw per day, dams lost weight on days 6-7, and a 13%
    reduction in body-weight gain compared with controls was evident on
    days 6-20; 150 mg/kg bw per day resulted in a 5% reduction in

    body-weight gain on days 6-20. Food consumption was reduced by 9% at
    150 mg/kg bw per day and by 13% at 350 mg/kg bw per day. There were no
    significant findings in dams  post mortem: uterine weights, litter
    size, resorptions, pre- and post-implantation losses, sex ratios, and
    fetal weights were similar in all groups. Isolated findings of
    malformations and anomalies were within the range in historical
    controls and showed no relationship to treatment. The overall
    incidence of variations was highest in controls, with no significant
    increase in any individual variation. The overall NOAEL for this study
    was 50 mg/kg bw per day on the basis of clinical signs (fur staining)
    and reduced maternal body weight at higher doses. The NOAEL for
    fetotoxicity was 350 mg/kg bw per day, the highest dose tested (Nemec,
    1996b).

    3.  Observations in humans

         Cases of dermatitis have been reported in workers handling fruit
    treated with ethoxyquin. A study with patch tests, cited in the 1969
    monograph, showed that the cause was a sensitization reaction rather
    than direct irritation (Wood, 1965).

         A number of reports (Burrows, 1975; van Hecke, 1977; Zachariae,
    1978; Brandao, 1983) have indicated that ethoxyquin is the probable
    cause of an often severe dermatitis seen in workers who handle animal
    feed containing ethoxyquin. Positive results in patch tests have been
    recorded in affected workers given challenge concentrations of as
    little as 0.01% ethoxyquin in petrolatum (Zachariae, 1978). The
    authors of some of the reports indicated that airborne contamination
    and light sensitivity are implicated. 

         A study cited in the 1969 monograph indicated that no evidence of
    skin irritation or sensitivity had been reported in 20 years of
    ethoxyquin production (Kelly, 1960). 

    Comments

         Published studies show that ethoxyquin is rapidly absorbed from
    the gastrointestinal tract of rats and mice, with peak blood levels
    within 1 h. Liver, kidney, and adipose tissue have the highest tissue
    concentrations. Excretion occurs predominantly via the urine and is
    rapid, with more than 85% of doses up to 25 mg/kg bw being excreted
    within 24 h. At 250 mg/kg bw, absorption and excretion are slowed,
    which is attributed to reduced gastric emptying, and only 50% of the
    dose is excreted within 24 h. Repeated oral doses of 25 mg/kg bw per
    day resulted in an excretion profile similar to that for single doses,
    but repeated administration of 250 mg/kg bw per day was reported to
    result in a profile similar to that for lower doses, indicating
    induction of metabolism, transport, and/or a return to normal gastric
    emptying. Biliary excretion and enterohepatic recirculation play a
    significant role in the toxicokinetics of ethoxyquin, more than 40% of
    an intravenous dose of 25 mg/kg bw being detected in the bile of
    bile-duct-cannulated rats. The metabolism of ethoxyquin involves
     O-deethylation or hydroxylation followed by conjugation as the

    sulfate or glucuronide. A proposed reaction scheme for the production
    of biliary metabolites involves epoxidation and the generation of
    reactive, electrophilic intermediates. No information on plant
    metabolites was available.

         Ethoxyquin has low acute toxicity when administered orally (LD50
    = 1700 mg/kg bw), dermally, or by inhalation. It is slightly
    irritating to the eyes and skin and had only very weak sensitizing
    potential when administered topically to guinea-pigs. Exposure to
    ethoxyquin in the workplace has been linked to allergic contact
    dermatitis, and the substance should be considered as a sensitizer in
    humans.

         WHO has not classified ethoxyquin for acute toxicity.

         The main target organ after repeated administration of ethoxyquin
    to rats for 28 days or more at doses of 50-1000 mg/kg bw per day was
    the kidney. Mechanistic studies with dietary concentrations equivalent
    to 250 mg/kg bw per day showed that the precise effects were dependent
    on the age at first exposure, were progressive, more severe in males
    than in females, and not reversible after 24 weeks of exposure. Other
    effects seen in rats exposed to ethoxyquin for 28 or 90 days at doses
    > 200 mg/kg bw per day were stained fur, brown urine, changes to
    haematological parameters, increased liver weights, and changes in
    clinical chemical parameters consistent with altered liver function.
    The overall NOAEL in the short-term studies in rats was 20 mg/kg bw
    per day.

         In dogs given capsules containing ethoxyquin for 90 days at 0, 2,
    4, 20, or 40 mg/kg bw per day, the liver was the primary target.
    Alterations in haematological parameters and clinical chemical changes
    indicative of altered liver function were seen at doses > 4 mg/kg bw
    per day, together with hepatocellular necrosis, vacuolation, and
    pigment deposition. Although staining indicated that the pigment was
    haemosiderin, a specific investigation showed it to be protoporphyrin
    IX. The overall NOAEL in short-term studies in dogs was 2 mg/kg bw per
    day. This is consistent with the results of an older, one-year study
    in dogs in which a NOAEL of 3 mg/kg bw per day was established on the
    basis of findings suggestive of effects on the kidney and liver at 10
    mg/kg bw per day.

         No modern long-term studies of toxicity or carcinogenicity have
    been performed. In studies summarized by the 1969 Meeting in which
    ethoxyquin was administered to dogs at 0 or 300 ppm in the diet for 5
    years or at 0, 3, 10, 50, or 100 mg/kg bw per day by gavage for one
    year, effects were observed in the liver and kidneys at doses of 10
    mg/kg bw per day and above. The NOAEL was 300 ppm, equivalent to 7.5
    mg/kg bw per day. A two-year study in rats that received dietary
    concentrations of 0, 62, 125, 250, 500, 1000, 2000, or 4000 ppm,
    published in 1959, gave no indication of carcinogenicity, with an
    overall NOAEL of 125 ppm, equivalent to 6 mg/kg bw per day; lesions in
    the kidney, liver, and thyroid gland were seen at higher doses.
    Mechanistic studies on tumour induction and promotion show that

    ethoxyquin induces both phase-I and phase-II xenobiotic metabolism.
    Although its incorporation into the diet at 8000 ppm after treatment
    with an  N-nitrosamine reduced the formation of preneoplastic foci in
    the liver, it increased the incidence of preneoplastic and neoplastic
    events in the kidney and urinary bladder. No significant increase in
    tumour incidence was seen after one year in mice that received four
    subcutaneous, near-lethal doses of ethoxyquin.

         Published reports of studies of bacterial mutagenicity indicate
    that ethoxyquin is not mutagenic in prokaryotic systems, but only
    limited details of the protocols and results were provided. No data
    were available on other genotoxic end-points.

         No modern study of reproductive toxicity has been performed in
    rodents. Three studies in which rats received 0, 125, 250, 375, 500,
    1000, or 1125 ppm in the diet, all with non-standard protocols, which
    were summarized by the 1969 Meeting, gave slightly contradictory
    results. Two of the studies, including the most extensive, apparently
    showed no effects on the aspects of reproduction investigated at doses
    up to 1125 ppm in the diet (equivalent to 56 mg/kg bw per day), while
    the other showed an increased incidence of stillbirths at 1125 ppm and
    decreased litter size at 375 ppm, with a NOAEL of 125 ppm (equivalent
    to 6 mg/kg bw per day).

         A modern two-generation study of reproductive toxicity in dogs
    given diets containing 0, 100, or 225 ppm showed that ethoxyquin had
    no effects on reproductive parameters at 225 ppm (equivalent to 5.6
    mg/kg bw per day), the highest dose tested. The clinical signs
    observed included dehydration, excess lachrymation, and evidence of
    hepatic toxicity, especially in bitches. The effects were seen at both
    doses and were consistent with the results of the short-term studies
    in dogs. The findings in bitches may have been related to increased
    consumption during gestation and lactation. The lowest dose tested,
    100 ppm, equivalent to 2.5 mg/kg bw per day, was considered to be a
    minimal effect level.

         A study of developmental toxicity in rats at 0, 50, 150, or 350
    mg/kg bw per day showed that ethoxyquin is not fetotoxic or
    teratogenic at doses up to 350 mg/kg bw per day. Maternal toxicity,
    stained fur, and reduced body-weight gain were seen at 150 and 350
    mg/kg bw per day. No studies of developmental toxicity have been
    performed in other species.

         An ADI of 0-0.005 mg/kg bw per day was established on the basis
    of the minimal-effect level of 2.5 mg/kg bw per day in the
    multigeneration study in dogs and a 500-fold safety factor to account
    for the lack of a NOAEL in this study and for the incompleteness of
    the database. The multigeneration study of reproductive toxicity was
    of longer duration and more recent than a 90-day study in dogs treated
    by gavage with a NOAEL of 2 mg/kg bw per day.

         An acute RfD was not allocated because ethoxyquin is of low acute
    toxicity. The Meeting concluded that the acute intake of residues is
    unlikely to present a risk to consumers.

    Toxicological evaluation

     Levels that cause no toxic effect

         Rat:      125 ppm, equivalent to 6 mg/kg bw per day (two-year
                   study of toxicity and carcinogenicity)
                   500 ppm, equivalent to 25 mg/kg bw per day
                   (two-generation study of reproductive toxicity)
                   50 mg/kg bw per day (maternal toxicity in a study of
                   developmental toxicity)
                   350 mg/kg bw per day (developmental toxicity)

         Dog:      2 mg/kg bw per day (general toxicity in a 90-day study
                   of toxicity)
                   3 mg/kg bw per day (one-year study of toxicity)
                   300 ppm, equivalent to 7.5 mg/kg bw per day (five-year
                   study of toxicity)
                   2.5 mg/kg bw per day (minimal effect level for general
                   toxicity in a two-generation study of reproductive
                   toxicity) 
                   5 mg/kg bw per day (reproductive performance; highest
                   dose tested)

     Estimate of acceptable daily intake for humans

         0-0.005 mg/kg bw

     Estimate of acute reference dose

         Not allocated (unnecessary)

     Studies that would provide information useful for continued 
     evaluation of the compound

         1.   Studies of genotoxicity in mammalian systems

         2.   A long-term study of toxicity and carcinogenicity in rats
              that complies with modern guidelines

         3.   Observations in humans

        List of end-points for setting guidance values for dietary and non-dietary exposure
                                                                                                 

    Absorption, distribution, excretion and metabolism in mammals

    Rate and extent of oral absorption         Rapid, > 50%
    Dermal absorption                          No relevant information
    Distribution                               Widely distributed; liver, kidney, adipose tissue
    Potential for accumulation                 Slight evidence of bioaccumulation
    Rate and extent of excretion               > 85% eliminated within 24 h
    Metabolism in animals                      Extensive; no parent compound detected in urine
    Toxicologically significant compounds      Metabolites considered of equivalent toxicity to parent 
    (animals, plants and environment)          compound

    Acute toxicity

    Rat :LD50 oral                             1700 mg/kg bw
    Rat: LD50 dermal                           > 2000 mg/kg bw
    Rat: LC50 inhalation                       > 2.0 mg/L (whole-body exposure)
    Skin irritation                            Slightly irritating
    Eye irritation                             Slightly irritating
    Skin sensitization                         Sensitizing

    Short-term toxicity

    Target/critical effect                     General toxicity in multigeneration study
    Lowest relevant oral NOAEL                 Dog: < 2.5 mg/kg bw per day (reproductive toxicity)
    Lowest relevant dermal NOAEL               No data
    Lowest relevant inhalation NOAEL           No data

    Genotoxicity                               No evidence of genotoxicity, but testing inadequate

    Long-term toxicity and carcinogenicity

    Target/critical effect:                    Inadequate data
    Lowest relevant NOAEL                      Inadequate data
    Carcinogenicity                            No evidence of carcinogenicity, but testing inadequate

    Reproductive toxicity

    Reproduction target / critical effect      No adverse effect on reproduction
    Lowest relevant reproductive NOAEL         Dog: 5 mg/kg per day, multigeneration study
    Developmental target /critical effect      No adverse effect on development
    Lowest relevant developmental NOAEL        Rat: 350 mg/kg/bw per day 

    Neurotoxicity/Delayed neurotoxicity        No data, but no concern from other studies

    Other toxicological studies                Not an initiator or promoter of liver tumours in 
                                               rats

                                               Possible increase in urinary bladder preneoplastic 
                                               and neoplastic changes

    Medical data                               Contact allergic dermatitis reported in food 
                                               handlers

    Summary                  Value                 Study                         Safety factor
    ADI                      0-0.005 mg/kg bw      Dog, multigeneration          500
                                                   study of reproductive 
                                                   toxicity
    Acute reference dose     Not allocated 
                             (unnecessary)
                                                                                                 
    
    References

    Brandao, F.M. (1983) Contact dermatitis to ethoxyquin.  Contact 
     Derm.,  9, 240.

    Buetler, T.M., Gallagher, E.P., Wang, C., Stahl, D.L., Hayes, J.D. &
    Eaton, D.L. (1995) Induction of phase I and phase II drug metabolising
    enzyme mRNA, protein and activity by BHA, ethoxyquin and Oltipraz.
     Toxicol. Appl. Pharmacol., 135, 45-57.

    Burka, L.T., Sanders, J.M. & Matthews, H.B. (1996) Comparative
    metabolism and disposition of ethoxyquin in rat and mouse. II.
    Metabolism.  Xenobiotica, 26, 597-611.

    Burrows, D. (1975) Contact dermatitis in animal feed mill workers.
     Br. J. Dermatol., 92, 167-170.

    Cox, A.J. (1953) 6-Ethoxy-2,2,4-trimethyl-1,2-dihydroquinone (EMHQ).
    Histological report on sections of rat tissues stained with
    haematoxylin-eosin. Unpublished report submitted by Monsanto Chemical
    Co., cited in 1969 JMPR monograph, Annex 1, reference 13.

    Derse, P. (1956) Assay report. Unpublished report from Wisconsin
    Alumni Research Foundation. Submitted to WHO by Monsanto Chemical Co.,
    cited in 1969 JMPR monograph; Annex 1, reference 13.

    Epstein, S.S., Fujii, K., Andrea, J. & Mantel, N. (1970)
    Carcinogenicity testing of selected food additives by parenteral
    administration to infant Swiss mice.  Toxicol. Appl. Pharmacol., 16,
    321-334.

    Gilman, M.R. & Voss, W.R (1995) Reproduction/chronic toxicology study
    of ethoxyquin with beagle dogs. Unpublished report HRP-MI #203-1.1
    from HRP Inc for Monsanto, St Louis, Missouri, USA. Submitted to WHO
    by the Oregon, Washington and California Pear Association.

    Hanzal, R.F. (1955) Final report and addendum. Chronic oral
    administration--dogs--metabolic studies. Unpublished report from
    Hazleton Laboratories. Submitted by Monsanto Chemical Co., cited in
    1969 JMPR monograph, Annex 1, reference 13.

    Hard, G.C. & Neal, G.E. (1992) Sequential study of the chronic
    nephrotoxicity induced by dietary administration of ethoxyquin in
    Fisher 344 rats  Fundam. Appl. Toxicol., 18, 278-287.

    van Hecke, E. (1977) Contact dermatitis to ethoxyquin in animal feeds.
     Contact Derm., 3, 341-352.

    Ito, N., Fukushima, S. & Tsuda, H. (1985) Carcinogenicity and
    modification of the carcinogenic response by BHA, BHT and other
    antioxidants.  CRC Crit. Rev. Toxicol., 15, 109-150.

    Joner, P.E. (1977) Butylhydroxyanisol (BHA), butylhyroxytoluene (BHT)
    and ethoxyquin (EMQ) tested for mutagenicity.  Acta Vet. Scand., 18,
    187-193.

    Kahl, R. & Netter, K.J. (1977) Ethoxyquin as an inducer and inhibitor
    of phenobarbital-type cytochrome-P450 in rat liver microsomes.
     Toxicol. Appl. Pharmacol., 40, 473-483.

    Kelly, R.E. (1960) Supplementary toxicity information on Santoquin
    (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline). Unpublished report
    prepared and submitted by Monsanto Chemical Co.; cited in 1969 JMPR
    monograph; Annex 1, reference 13.

    Manson, M.M., Green, J.A., Wright, B.J. & Carthew, P. (1992) Degree of
    ethoxyquin-induced nephrotoxicity in rat is dependent on age and sex.
     Arch. Toxicol., 66, 51-56.

    Masui, T., Tsuda, H., Inoue, K., Ogiso, T. & Ito, N. (1986) Inhibitory
    effects of ethoxyquin, 4,4'-diaminophenylmethane and acetaminophen on
    rat hepatocarcinogenesis.  Jpn. J. Cancer Res. (Gann), 77, 231-237.

    Miyata, Y., Fukushima, S., Hirose, M., Masui, T. & Ito, N. (1985)
    Short-term screening of promoters of bladder carcinogenesis in
    N-butyl-n-(4-hydroxy)-nitrosamine-initiated, unilaterally
    ureter-ligated rats.  Jpn. J. Cancer Res. (Gann), 76, 828-834.

    Monsanto (1966) Five year Santoquin feeding study in dogs. Unpublished
    collection of reports prepared and submitted by Monsanto Chemical Co.,
    cited in 1969 JMPR monograph; Annex 1, reference 13.

    Naas, D.J. (1996a) A 90-day oral (gavage) toxicity study of ethoxyquin
    in rats, Unpublished report No. WIL-273011 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association,

    Naas. D.J. (1996b) A 28-day oral (capsule) dose range-finding study of
    ethoxyquin in dogs. Unpublished report No. WIL-273012 from WIL
    Research Laboratories, Inc., Ohio, USA. Submitted to WHO by the
    Oregon, Washington and California Pear Association.

    Naas. D.J. (1996c) A 90-day oral (capsule) toxicity study of
    ethoxyquin in dogs. Unpublished report No. WIL-273013 from WIL
    Research Laboratories, Inc., Ohio, USA. Submitted to WHO by the
    Oregon, Washington and California Pear Association.

    Naas, D.J. (1997) A 28-day oral (gavage) toxicity study of ethoxyquin
    in rats. Unpublished report No. WIL-273010 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association,

    Nemec, M.D. (1996a) A dose range-finding developmental toxicity study
    of ethoxyquin in rats. Unpublished report No. WIL-273008 from WIL
    Research Laboratories, Inc., Ohio, USA. Submitted to WHO by the
    Oregon, Washington and California Pear Association.

    Nemec, M.D. (1996b) A developmental toxicity study of ethoxyquin in
    rats. Unpublished report No. WIL-273009 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Ohta, T., Moriya, M., Kaneda, K., Watanabe, K., Miyazawa, T.,
    Sugiyama, F. & Shirasu, Y. (1980) Mutagenicity screening of feed
    additives in the microbial system.  Mutat. Res., 77, 21-30. 

    Sanders, J.M., Burka, L.T. & Matthews, H.B. (1996) Comparative
    metabolism and disposition of ethoxyquin in rat and mouse. I.
    Disposition.  Xenobiotica, 26, 583-595.

    Ulrich, C.E. (1996) Acute inhalation toxicity study of ethoxyquin in
    rats. Unpublished report No. WIL-273006 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Varsho, B.J. (1995a) Acute oral toxicity study of ethoxyquin in albino
    rats. Unpublished report No. WIL-273001 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Varsho, B.J. (1995b) Acute dermal toxicity study of ethoxyquin in
    albino rats. Unpublished report No. WIL-273002 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Varsho, B.J. (1995c) Primary eye irritation study of ethoxyquin in
    albino rabbits. Unpublished report No. WIL-273004 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Varsho, B.J. (1995d) Primary dermal irritation study of ethoxyquin in
    albino rabbits. Unpublished report No. WIL-273003 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Varsho, B.J. (1995e) Skin sensitization study of ethoxyquin in albino
    guinea pigs. Unpublished report No. WIL-273005 from WIL Research
    Laboratories, Inc., Ohio, USA. Submitted to WHO by the Oregon,
    Washington and California Pear Association.

    Wilson, R.H. (1956) Final report: Reproduction study in rats receiving
    Santoquin. Unpublished report of Western Regional Utilization Research
    Branch, US Department of Agriculture. Submitted to WHO by Monsanto
    Chemical Co.; cited in 1969 JMPR monograph; Annex 1, reference 13.

    Wilson, R.H. & DeEds, F. (1959) Toxicity studies on the antioxidant
    6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline.  J. Agric. Food 
     Chem., 7, 203-206.

    Wood, W.S. (1965) Untitled report of dermatitis cases in fruit
    handlers. Unpublished report submitted by Monsanto Chemical Co., cited
    in 1969 JMPR monograph; Annex 1, reference 13.

    Zachariae, H. (1978) Ethoxyquin dermatitis.  Contact Derm., 4,
    117-118.

    Zeiger, E. (1993) Mutagenicity of chemicals added to foods.  Mutat. 
     Res., 290, 53-61.
    


    See Also:
       Toxicological Abbreviations
       Ethoxyquin (FAO/PL:1969/M/17/1)
       Ethoxyquin (JMPR Evaluations 2005 Part II Toxicological)