IPCS INCHEM Home


    Pesticide residues in food -- 1999



    Sponsored jointly by FAO and WHO
    with the support of the International Programme
    on Chemical Safety (IPCS)



    Toxicological evaluations




    Joint meeting of the
    FAO Panel of Experts on Pesticide Residues
    in Food and the Environment
    and the
    WHO Core Assessment Group

    Rome, 20-29 September 1999

    PYRIPROXYFEN

    First draft prepared by
    K. Fujimori
    National Institute of Health Sciences, Tokyo, Japan


            Explanation
            Evaluation for acceptable daily intake
                Biochemical aspects
                    Absorption, distribution, and excretion
                    Biotransformation
                Toxicological studies
                    Acute toxicity
                    Short-term studies of toxicity
                    Long-term studies of toxicity and carcinogenicity
                    Genotoxicity
                    Reproductive toxicity
                        Multigeneration reproductive toxicity
                        Developmental toxicity
                    Studies on metabolites
                        Acute toxicity
                        Genotoxicity
            Comments
            Toxicological evaluation
            References


    Explanation

         Pyriproxyfen, 4-phenoxyphenyl  (RS)-2-(2-pyridyloxy)propyl
    ether, is a 2-phenoxy phenoxy oxime used as an insecticide which acts
    as an insect growth regulator. It is intended for use as a spray in
    the control of arthropods, including cockroaches and fleas, on crops,
    dumps and indoors. Pyriproxyfen was evaluated for the first time by
    the Meeting.

    Evaluation for Acceptable Daily Intake

    1.  Biochemical aspects

    (a)  Absorption, distribution, and excretion

         In a study carried in compliance with good laboratory practice
    (GLP), groups of five male and five female Sprague-Dawley rats were
    given pyriproxyfen labelled uniformly with 14C on the phenoxyphenyl
    ring (radiochemical purity, > 99%) as a solution in corn oil orally
    by gavage at doses of 2 or 1000 mg/kg bw, with or without pretreatment
    with unlabelled pyriproxyfen (2 mg/kg bw). Radiolabel was excreted
    predominantly in the faeces (90%) at both doses, urinary excretion
    representing 4-8% of the administered dose over 48 h. The total
    recovery of radiolabel in the excreta over 168 h was 96-98% of the
    dose, and the residual radiolabel in the tissues and carcass

    represented no more than 0.3% of the dose. The tissue with the highest
    concentration of radiolabel was fat, which contained 0.01 g/g as
    equivalent. Pretreatment with unlabelled pyriproxyfen before
    administration of 2 mg/kg bw per day for 14 days increased the
    residual radiolabel in the tissues slightly but did not change the
    excretion pattern. There was no significant sex- or dose-related
    difference in excretion rates or in the tissue distribution of
    radiolabel.

         In a further study, groups of three male and three female
    Sprague-Dawley rats with cannulated bile ducts were given
    [14C-phenoxyphenyl]pyriproxyfen orally at a single dose of 2 mg/kg
    bw. Biliary excretion of the radioactive material represented 34-37%
    of the dose within 48 h of administration. Urinary excretion
    represented 2-3% of the dose and faecal excretion 38-51% (Isobe et
    al., 1988a; GLP: Matsunaga et al. 1995). These experiments suggest
    that as much as 50% of an oral dose of pyriproxyfen is not absorbed.

         Groups of five male and five female Sprague-Dawley (Crl-CD) rats
    were given pyriproxyfen labelled with 14C in the pyridyl ring at a
    dose of 2 or 1000 mg/kg bw in a study that complied with GLP.
    Radiolabel was excreted predominantly in the faeces, representing
    about 90% of the dose, and urinary excretion comprised 5-11% of the
    dose over 48 h. Total recovery of radiolabel in the excreta after
    168 h represented 92-99% of the dose. Expired air contained < 0.5% of
    the dose over 48 h. The residual radiolabel in the tissues and carcass
    represented no more than 0.3% of the dose 168 h after administration.
    The tissue with the highest concentration of radiolabel was fat, with
    0.01-0.02 g/g as equivalent. No significant differences associated
    with the position of the label, sex or dose were seen in the excretion
    rates or tissue distribution (Yoshino, 1993a; Matsunaga et al., 1995)

         In another study that complied with GLP, groups of three male and
    three female Sprague-Dawley rats were given
    [14C-phenoxyphenyl]pyriproxyfen orally at a single dose of 2 mg/kg
    bw, and radiolabel in tissues was determined 2, 4, 8, 12, 24, 48, and
    72 h after dosing. The peak concentration of radiolabel in blood was
    observed 8 h after dosing. The concentrations in blood were four times
    higher in males than in females, with a terminal half-time of 10-14 h.
    The time to peak concentration in most tissues was 2-8 h after dosing,
    while that in fat was 12-24 h. At the respective peak time, the
    concentration in the liver was the highest (2.1-2.4 mg/g at 8 h as
    equivalent) of the tissues examined; however, 72 h after dosing, the
    highest concentration was found in fat (0.08-0.09 mg/g tissue as
    equivalent). The concentration in tissues other than liver (0.02-0.03
    mg/g tissue as equivalent) was < 0.01 mg/g as equivalent 72 h after
    dosing. The half-time of radiolabelled material in the tissues was
    8-35 h (Isobe et al., 1988b; Matsunaga et al., 1995).

         Groups of three male and three female Sprague-Dawley rats were
    given [14C-phenoxyphenyl]-pyriproxyfen orally at a single dose of
    1000 mg/kg bw, and radiolabel in tissues was determined 2, 4, 8, 12,
    24, 48, and 72 h after dosing in a study that complied with GLP. The

    peak concentration in blood was achieved after 8 h. The concentrations
    of radiolabel in blood in males were six times higher than in females.
    The time to peak concentration in all tissues except fat was 4 h in
    males and 8 h in females. At the respective peak time, the highest
    concentration was found in liver (160-320 mg/g as equivalent at 8 h,
    decreasing to 8-12 mg/g at 72 h). The highest residual concentration
    72 h after dosing was in fat (45-46 mg/g tissue as equivalent). The
    concentration of radiolabel in fat peaked 12-24 h after dosing and
    decreased with a half-time of 23 h in males and 35 h in females. The
    residual concentrations in other tissues were < 10 mg/g tissue 72 h
    after dosing, and the half-time was 5-17 h. There was no dose-related
    difference in the tissue distribution of pyriproxyfen (Yoshino, 1993b;
    Matsunaga et al., 1995).

    (b)  Biotransformation

          Mice 

         Groups of three male and three female mice were given
    [14C-pyridyl]pyriproxyfen orally at a dose of 2 or 1000 mg/kg bw.
    Faecal excretion represented 78-90% of the low dose and 64-65% of the
    high dose, and urinary excretion 10-27% and 35-37%, respectively, over
    7 days. Complete recovery of radiolabel (100-105% of the dose) was
    observed over that time. Twelve metabolites were identified by
    thin-layer chromatography (TLC) and high-performance liquid
    chromatography (HPLC). The major metabolite in faeces was
    4'-hydroxypyriproxyfen (36-38% of the low dose and 13-15% of the high
    dose); minor metabolites were 4-hydroxyphenyl  (RS)-2-(2-pyridyloxy)
    propyl ether (3%) and  (RS)-2hydroxypropyl 4-phenoxyphenyl ether
    (1-3%). The urinary metabolites were 4'-hydroxypyriproxyfen (0-5%),
    4'-hydroxypyriproxyfen glucuronide (3-13% of the low dose, 18-28% of
    the high dose), and  (RS)-2-hydroxypropyl 4-phenoxyphenyl ether
    sulfate (3-6% of dose). The percent of the dose represented by
    glucuronide and sulfate conjugates in urine was higher in mice than in
    rats, but no other species difference in the metabolic pathways of
    pyriproxyfen were seen. There was no difference in 4'-hydroxylation by
    sex (Yoshino et al., 1995).

          Rats 

         The biotransformation of [14C-phenoxyphenyl]pyriproxyfen in
    rats was investigated in samples from the study of Isobe et al.
    (1988a,b), described above. After oral administration, more than 26
    metabolites were detected in faeces and urine by TLC. The major
    metabolite was 4'-hydroxypyriproxyfen (25-48% of the dose). Total
    recovery of radiolabel in faeces and urine represented 93-96% of the
    dose, and 31-37% was detected as parent compound in the faeces 48 h
    after the low or high dose, while no parent compound was detected in
    urine. Ten metabolites, including conjugates, were identified by TLC
    in excreta, all 10 occurring in faeces at the high dose and two in
    urine. The major metabolite identified in feces was
    4'-hydroxypyriproxyfen, formed by oxidative metabolism of the phenyl
    ring, and the others were oxidative products (2-hydroxypyriproxyfen

    and 4',5''-hydroxypyriproxyfen), the products of ether cleavage
    ( (RS)-2-hydroxypropyl 4-phenoxyphenyl ether, 4-phenoxyphenol, and
    their hydroxylated metabolites), and their conjugates (sulfates). The
    metabolites identified in urine were sulfate conjugates of
    4'hydroxypyriproxyfen (0.4-1.0% of the low dose, 0.5-1.0% of the high
    dose) and 4'-hydroxy-4-phenoxyphenol (0.5-3.0% of the low dose,
    0.3-1.6% of the high dose). Less parent compound was found in faeces
    after repeated oral dosing, but repeated treatment with the vehicle,
    corn oil, caused a similar decrease. The percentage of the dose
    recovered as 4'-hydroxypyriproxyfen in faeces was higher in females
    than in males. The major metabolites identified in fat, liver, kidney,
    and blood collected 2, 4, 8, 12, 24, 48, and 72 h after administration
    of 2 mg/kg bw of radiolabelled pyriproxyfen were
    4',5''-hydroxypyriproxyfen sulfate in blood and 4-hydroxy- and
    4',5''-hydroxypyriproxyfen in kidney and liver. At the time of peak
    concentration, the parent compound represented 0% in males and 9% in
    females of the total radiolabel present. A greater percentage of the
    dose was recovered as 4'-hydroxypyriproxyfen in the liver of females
    than males. In the kidney, sulfate conjugates represented a larger
    percentage of the dose in males than in females. Unmetabolized
    pyriproxyfen represented 89-93% of the radiolabel in the extractable
    fraction of fat (90% was extracted) (Isobe et al., 1988a,b).

         The biotransformation of [14C-pyridyl]pyriproxyfen in rats was
    also investigated in samples from the study of Yoshino (1993a),
    described above. More than 13 metabolites were detected in faeces and
    urine by TLC and HPLC, with nine, including conjugates, in faeces and
    four in urine. The major metabolite in faeces was
    4'-hydroxypyriproxyfen (23-47% of the dose), and the other metabolites
    were oxidative products (2-hydroxy- and 4',5''-hydroxypyriproxyfen),
    the products of ether cleavage (4-hydroxyphenyl
     (RS)-2-(2pyridyloxy)propyl ether and
     (RS)-2-(2-pyridyloxy)-propionic acid), and their sulfate or
    glucuronide conjugates. The metabolites identified in urine were
    4'-hydroxypyriproxyfen (0% of the low dose, 1.0-5.6% of the high dose)
    and its sulfate conjugate (0.3-0.4% of the low dose, 0% of the high
    dose), the sulfate conjugate of 4',5''-hydroxypyriproxyfen (0% of the
    low dose, 0.1-0.2% of the high dose), and  (RS)-2-(2-pyridyloxy)
    propionic acid (1-1.7% of the low dose, 0% of the high dose) (Yoshino,
    1993a)

         These studies indicate that the major route of metabolism of
    pyriproxyfen is hydroxylation, with cleavage of the ether bonds and
    conjugation as minor routes. Hydroxylation occurs primarily at the 4'
    position of the phenyl ring (phenoxy group) and subsequently at the
    5'' position of the pyridyl group. Conjugation produces mainly the
    respective sulfates of the oxidative metabolites. There was no
    evidence of induction of metabolism by pretreatment with pyriproxyfen.
    The pattern of metabolites in the excreta and tissues of males and
    females suggests a considerable sex difference in metabolic activity.
    There were no significant differences in the metabolic pathway by dose
    or frequency of dosing. The proposed metabolic pathway for
    pyriproxyfen in various species is shown in Figure 1.

    FIGURE 1

          Lactating goats 

         Lactating goats  (Capra hircus, weighing 51-57 kg) were given
    [14C-phenoxyphenyl]-pyriproxyfen (purity, 99.5%) in gelatin capsules
    at a dose of 1.8-2.0 or 20 mg/animal per day for 5 consecutive days,
    for a total dose of 100 mg. The animals were killed within 6 h of the
    last dose. Faeces, urine, and milk were collected twice daily and
    analysed. Metabolites were purified from extracts of tissues or
    excreta by HPLC and identified by TLC and/or mass spectral analysis.
    The study was carried out according to GLP. Elimination reached a
    plateau by the third day. The percentages of total radiolabel
    recovered 1 day after the last dose were 17-18% in urine, 58% in
    faeces, and 0.3-0.8% in milk. The metabolites identified in milk
    extracts were 4'-hydroxypyriproxy-fen sulfate (51% of the radiolabel
    present), 4'-hydroxypyriproxyfen (2%), 4-phenoxyphenol sulfate (10%),
    4'-hydroxy-4-phenoxyphenol sulfate (8%),
    4'-hydroxy- (RS)-2-hydroxypropyl 4-phenoxyphenyl ether sulfate (3%),
    and 4-hydroxyphenyl  (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen
    (8%). Metabolites found in both liver and kidney were
    4'-hydroxypyriproxyfen sulfate, 5''-hydroxypyriproxyfen-sulfate,
     (RS)-2-hydroxypropyl 4-phenoxyphenyl ether,
    4'-hydroxy (RS)-2-hydroxypropyl 4-phenoxyphenyl ether, and
    4-hydroxyphenyl  (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen. In
    addition, 4'-hydroxypyriproxyfen and 5''-hydroxypyri-proxyfen were
    identified in liver, and 4-phenoxyphenol  sulfate and
    4'-hydroxy-4-phenoxyphenol in kidney. The metabolites identified in
    the faecal samples were 4'-hydroxypyriproxyfen (39% of the radiolabel
    present), 5''-hydroxypyriproxyfen (6%),
    4'-hydroxy- (RS)-2-hydroxypropyl 4-phenoxyphenyl ether (5%),
     (RS)-2-hydroxypropyl 4phenoxyphenyl ether, and 4-hydroxyphenyl
     (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen. Parent compound
    accounted for 11-13% of the dose in faeces, The major metabolites in
    urine were 4-phenoxyphenol (36% of the radiolabel present),
    4-phenoxyphenol sulfate (15%), 4'-hydroxy-4-phenoxyphenol (14%), and
    4'-hydroxy-4-phenoxyphenol  sulfate (17%) (Panthani et al., 1996a)

         In another study that conformed to GLP, lactating goats
    ( Capra hircus, weighing 39-46 kg) were given
    [14C-pyridyl]pyriproxyfen (purity, 97.6% ) in gelatin capsules at a
    dose of 1.8-1.9 or 20 mg/animal per day for 5 consecutive days. The
    animals were killed within 6 h of the last dose. Faeces, urine, and
    milk were collected twice daily and analysed by HPLC and TLC and/or
    mass spectrometry. The total radiolabel recovered represented 17-18%
    of the dose in urine, 58% in faeces, and 0.4-0.8% in milk. The major
    metabolites identified in milk extracts were 4'-hydroxypyriproxyfen
    sulfate (35% of the radiolabel present) and 2,5-dihydroxypyridine
    conjugate (29%), with smaller quantities of 4'-hydroxypyriproxyfen and
    4-hydroxyphenyl  (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen. The
    major metabolites identified in liver and kidney were
    4'-hydroxypyriproxyfen sulfate, 2,5-dihydroxypyridine conjugate, and
     (RS)-2-(2-pyridyoxy) propanol conjugates. The major metabolites
    identified in the urine were 4'-hydroxypyriproxyfen sulfate,
     (RS)-2-(2-pyridyloxy) propionic acid, and 2,5-dihydroxypyridine

    conjugate. The metabolites identified in the faecal samples were
    4'-hydroxypyriproxyfen (43%), 5''-hydroxypyriproxyfen (5%), and
    4-hydroxyphenyl  (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen
    (5%). These two studies indicate that the primary routes of metabolism
    in goats are hydroxylation of the 4'  position of the phenoxyphenyl
    ring and the 5'' position of the pyridyl ring, cleavage of the ether
    bonds, oxidation of the methylene moiety, and sulfate conjugation of
    the 4'-hydroxyphenoxyphenyl moiety. There is thus no difference
    between rats and goats in the metabolic pattern of pyriproxyfen
    (Panthani et al., 1996b)

          Chickens 

         Laying Leghorn hens  (Gallus domesticus) were given
    [14C-phenoxyphenyl]pyriproxyfen (purity, 99.1%) by gelatin capsule
    at a concentration equivalent to 10 ppm in the feed for 8 consecutive
    days and were killed within 4 h of the last dose. Excreta were
    collected once daily and analysed by HPLC and TLC and/or mass
    spectrometry. The study complied with GLP. The metabolites identified
    in liver and kidney were free 4'-hydroxypyriproxyfen and its sulfate
    conjugate, free 4'-hydroxy-4-phenoxyphenol and its sulfate conjugate,
    free 4'-hydroxy- (RS)-2-hydroxypropyl-4-phenoxyphenyl ether and its
    sulfate conjugate, 4-phenoxyphenol sulfate,
    4-hydroxyphenyl- (RS)-2-(2-pyridyloxy)propyl ether pyriproxyfen, and
     (RS)-2-hydroxypropyl-4-phenoxyphenyl ether. Metabolites identified
    in excreta samples were 4'-hydroxypyriproxyfen, free and conjugated
    4'-hydroxy-4-phenoxyphenol, free and conjugated
    4'-hydroxy- (RS)-2-hydroxy-propyl 4-phenoxyphenyl ether,
    4-hydroxyphenyl  (RS)-2-(2pyridyloxy)propyl ether pyriproxyfen,
    5''-hydroxypyriproxyfen,  (RS)-2-hydroxypropyl-4-phenoxyphenyl ether,
    and 4-phenoxyphenol (Panthani et al., 1996c)

         Laying Leghorn hens  (Gallus domesticus) were given
    [14C-pyridyl]pyriproxyfen (purity, 98.2%) by gelatin capsule at a
    concentration equivalent to 10 ppm in the feed for 8 consecutive days
    and were killed within 4 h of the last dose. Excreta were collected
    once daily and analysed by HPLC and TLC and/or mass spectrometry. The
    study complied with GLP. The metabolites identified in liver and
    kidney were free and conjugated 4'-hydroxypyriproxyfen,
    2-hydroxypyridine, free and conjugated 5''-hydroxypyriproxyfen,
    4-hydroxyphenyl- (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen, and
     (RS)-2-(2-pyridyloxy)propionic acid. The metabolites identified in
    excreta were  (RS)-2-(2-pyridyloxy) propionic acid,
    4'-hydroxypyriproxyfen, 4-hydroxyphenyl  (RS)-2-(2-pyridyloxy)propyl
    ether pyriproxyfen, 5''-hydroxypyriproxyfen, and 2-hydroxypyridine.
    These two studies indicate that the routes of metabolism in laying
    hens are hydroxylation at the 4' position of the phenoxyphenyl ring
    and at the 5'' position of the pyridyl ring, cleavage of the ether
    linkages, oxidation of the methylene moiety of the side-chain, and
    sulfation of the 4'-hydroxyphenoxyphenyl moiety (Panthani et al.,
    1996d)

          In vitro 

         The metabolism of pyriproxyfen in rats and mice was investigated
     in vitro in samples of 10 000   g supernatant (S10) prepared from
    kidney, lungs, and small intestine of 7-week-old Sprague-Dawley rats
    and ICR mice. Hepatic microsomal and cytosolic fractions were prepared
    by an established method (centrifugation of S10 at 105 000   g), and
    microsomal, S10, or cytosolic fractions were incubated with
    [14C-phenoxyphenyl]pyriproxyfen at a concentration of 0, 0.05, 0.1,
    0.5, or 1.0 mmol/L with b-NADPH as a cofactor. The reaction mixtures
    were analysed by TLC. Pyriproxyfen was not metabolized by any of the
    S10 preparations; it was almost completely metabolized by microsomal
    fractions from liver but only very slightly by hepatic cytosol. Most
    of the major metabolites identified in rats  in vivo were observed
     in vitro. There was no species difference in the major metabolic
    reactions. The intrinsic clearance calculated from Lineweaver-Burk
    plots revealed sex-related differences in metabolic reactions in rats
    but not in mice, and 5''-hydroxylation was observed only in male rats
    and not in mice of either sex. The intrinsic clearance for microsomal
    4'-hydroxylation in female rats was twice that in males, but was not
    different in male and female mice. Incubation of a hepatic microsomal
    fraction from male rats with antisera against male-specific forms of
    cytochrome P450 (CYP2C11 or CYP2C13) revealed that members of the
    CYP2C family, the expression of which is sex-dependent in rats, are
    involved in the major hydroxylation reactions of pyriproxyfen.
    Antiserum against CYP2C11 inhibited all of the major metabolic
    reactions of the hepatic microsomal fraction from male rats (> 88%
    inhibition). The antiserum against CYP2C13 also inhibited all
    reactions (25-64% inhibition) except 4'-hydroxylation (Yoshino et al.,
    1996).

    2.  Toxicological studies

    (a)  Acute toxicity

         The results of studies of the acute toxicity of pyriproxyfen are
    summarized in Table 1. Pyriproxyfen dissolved in corn oil was
    administered orally in a volume of 10 ml/kg bw to ICR (Crj:CD-1) mice
    at doses of 1000, 2000, or 5000 mg/kg bw and to Sprague-Dawley
    (Crj:CD) rats at 1000, 2500, or 5000 mg/kg bw. In mice, pyriproxyfen
    reduced spontaneous motor activity and caused ataxia, abnormal
    respiration, and death in males at 2000 mg/kg bw and in animals of
    each sex at 5000 mg/kg bw. Transiently decreased body weight was
    observed in males at 5000 mg/kg bw. Deaths occurred in two males at
    2000 mg/kg bw and two at 5000 mg/kg bw in males and in one female at
    5000 mg/kg bw. In rats, pyriproxyfen caused a decrease in body-weight
    gain, decreased spontaneous activity, soft stools, and diarrhoea in
    males at 2500 mg/kg bw and in animals of each sex at 5000 mg/kg bw,
    but no deaths. Necropsy revealed no abnormal changes in the organs of
    mice or rats. In dogs, oral administration of pyriproxyfen in capsules
    caused no deaths at doses up to 5000 mg/kg bw. The only clinical sign,
    occasional vomiting for the first 24 h, was observed at the highest
    dose. Dermal application of 2000 mg/kg bw of pyriproxyfen dissolved in

    corn oil (5 or 10 ml/kg bw) caused no deaths or signs of clinical
    toxicity in ICR mice or Sprague-Dawley rats. Exposure of ICR mice or
    Sprague-Dawley rats to a mist aerosol of pyriproxyfen dissolved in
    corn oil at concentrations of 0.6 or 1.3 mg/L for 4 h caused no deaths
    or pathological changes. The mass median aerodynamic diameter of the
    particles was 0.8-0.9 m. At the high concentration, salivation and
    urinary incontinence were observed in rats 4 h after the start of
    inhalation, and irregular respiration was observed in mice. These
    clinical signs disappeared within 1 h of cessation of exposure.

    (b)  Short-term studies of toxicity

          Mice 

         Groups of 10 male and 10 female ICR (Crj:CD-1) mice were given
    diets containing technical-grade pyriproxyfen (purity, 95.3%) at
    concentrations of 0, 200, 1000, 5000, or 10 000 ppm, equal to 0, 28,
    150, 840, and 2000 mg/kg bw per day for males and 0, 38, 200, 960, and
    2300 mg/kg bw per day for females, for 13 weeks. The observations
    included clinical signs, mortality, food and water consumption, body
    weight, clinical chemical parameters including serum enzymes, urinary
    and haematological parameters, organ weights, and gross and
    histopathological appearance. The serum enzymes assayed were alanine
    aminotransferase), aspartate aminotransferase, and gamma-glutamyl
    transpeptidase. Blood samples were collected shortly before
    termination of the study. The study conformed to GLP.

         Death occurred in two males at 5000 ppm and in seven males and
    nine females at 10 000 ppm (one of the deaths in males was not
    treatment-related). The clinical signs observed in the animals that
    died prematurely were emaciation, hunched appearance, and few or no
    faeces. There were no treatment-related clinical signs in the mice
    that survived. Terminal body weights were significantly reduced in
    males at 5000 ppm (89% of control) and at 10 000 ppm (69% of control);
    the body weights of females were reduced at 5000 ppm during the first
    half of the study but were comparable to control values (97% of
    control) by the end. The water consumption of males at the two higher
    doses was significantly increased, but food consumption was not
    affected by treatment. There were significant decreases in erythrocyte
    parameters, including cell count, haemoglobin concentration,
    haematocrit, mean cell volume, and mean cell haemoglobin value, in
    animals at 5000 and 10 000 ppm. Platelet counts were significantly
    increased in animals of each sex at 5000 ppm and in males at 10 000
    ppm. Significant increases in total cholesterol concentration were
    observed in females at doses > 1000 ppm: 130% at 1000 ppm, 210% at
    5000 ppm, and 140% of control values at 10 000 ppm. In males, the
    activities of aspartate and alanine aminotransferases were increased
    by up to twofold but reached significance only at 5000 ppm.
    gamma-Glutamyl transpeptidase activity showed slight, nonsignificant
    changes in some groups. The absolute weight of the liver was
    significantly increased in females at 5000 ppm (120% at 5000 ppm and
    160% of control values at 10 000 ppm) but not in males at any dose.
    Microscopic examination revealed histomorphological alterations of the


        Table 1. Acute toxicity of pyriproxyfen

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

    Mouse      ICR               M&F      Oral           > 5000          97.2      Suzuki et al. (1987a)
    Rat        Sprague-Dawley    M&F      Oral           > 5000          97.2      Suzuki et al. (1987b)
    Dog        Beagle            M&F      Oral           > 5000          97.2      Nakano et al. (1986)
    Mouse      ICR               M&F      Dermal         > 2000          97.2      Suzuki et al. (1987c)
    Rat        Sprague-Dawley    M&F      Dermal         > 2000          97.2      Suzuki et al. (1987d)
    Mouse      ICR               M&F      Inhalation     > 1.3           97.0      Suzuki et al. (1987e)
    Rat        Sprague-Dawley    M&F      Inhalation     > 1.3           97.0      Kawaguchi et al. (1987)
                                                                                                            

    These studies were conducted according to good laboratory practice.
    


    kidney comprising tubular nephrosis with microcytosis and dilatation
    of the renal tubules and focal mineralization and dilatation of the
    renal pelvis in males at 5000 ppm and in animals of each sex at 10 000
    ppm. There were no treatment-related morphological changes in the
    liver. The NOAEL was 1000 ppm, equal to 150 mg/kg bw per day, on the
    basis of effects on erythrocyte parameters, deaths, decreased body
    weight, histomorphological alterations in the kidney, and increased
    absolute liver weight at higher doses (Cox et al., 1990).

          Rats 

         Groups of 10 male and 10 female Sprague-Dawley (Crl:CD) rats
    received diets containing technical-grade pyriproxyfen (purity, 95.3%)
    at concentrations of 0, 400, 2000, 5000, or 10 000 ppm, equal to 0,
    23, 120, 310, and 640 mg/kg bw per day for males and 0, 28, 140, 360,
    and 780 mg/kg bw per day for females, for 13 weeks. The observations
    included clinical signs, deaths, body weight, food and water
    consumption, ophthalmological, clinical chemical, haematological, and
    urinary parameters, organ weights, and gross and histopathological
    appearance. The clinical chemical examinations included assays for the
    serum enzymes alkaline phosphatase, aspartate and alanine
    aminotransferases, and gamma-glutamyl transpeptidase. Blood samples
    were collected at the end of the study.

         There were no treatment-related deaths, toxic signs, or
    ophthalmological changes at any dose, and no changes in food or water
    consumption. The body weights of animals of each sex were
    significantly decreased at doses > 5000 ppm (91% of control at 5000
    ppm and 88% at 10 000 ppm at termination). Erythrocyte parameters
    including cell count, haemoglobin concentration, and haematocrit were
    significantly decreased in animals at doses > 5000 ppm and in males
    also at 2000 ppm. The mean cell volume was reduced in females at 2000
    and 10 000 ppm by < 10%. There was no significant effect on platelet
    count. The total cholesterol concentration was dose-dependently,
    significantly increased in males at doses > 2000 ppm (150% at 2000
    ppm, 200% at 5000 ppm, and 210% of control values at 10 000 ppm) and
    in females at doses > 5000 ppm (130% at 5000 ppm and 180% of
    control values at 10 000 ppm). The serum phospholipid concentration
    was also significantly increased in males at doses > 2000 ppm (130%
    at 2000 ppm, 180% at 5000 ppm, and 180% of control values at 10 000
    ppm) and in females at 10 000 ppm (160% of control value).
    Significantly increased gamma-glutamyl transpeptidase activity was
    observed in animals at 10 000 ppm, but the activities of the other
    serum enzymes were not significantly affected. Significant increases
    in the absolute weight of the liver were observed in animals at doses
    > 5000 ppm (110% at 2000 ppm, 130% at 5000 ppm, and 140% of control
    values at 10 000 ppm in males and 100% at 2000 ppm, 120% at 5000 ppm,
    and 140% of control values at 10 000 ppm in females), and the relative
    weight of the liver was significantly increased in males at 2000 ppm
    and in animals of each sex at doses > 5000 ppm (120% at 2000 ppm,
    140% at 5000 ppm, and 170% of control values at 10 000 ppm in males
    and 130% at 5000 ppm and 160% of control values at 10 000 ppm in
    females). Significant increases in the relative weight of the kidney

    were observed in animals at 10 000 ppm, but the absolute weights were
    comparable to those of controls at all doses. Histopathological
    examination revealed dose-dependent increases in cytoplasmic changes
    in the liver in all treated groups (1/10 at 0 ppm, 2/10 at 400 ppm,
    6/10 at 2000 ppm, 10/10 at 5000 ppm, and 9/10 at 10 000 ppm in males
    and 1/10 at 0 ppm, 2/10 at 400 ppm, 6/9 at 2000 ppm, 7/10 at 5000 ppm,
    and 9/10 at 10 000 ppm in females). The cytoplasmic changes consisted
    of slight, often equivocal increases in cytoplasmic content reflected
    in a visibly reduced nucleus:cytoplasm ratio and diminution of
    sinusoidal spaces. The NOAEL was 400 ppm, equal to 23 mg/kg bw per
    day, on the basis of mild anaemia, increased incidences of minimal
    hepatic abnormalities, relative liver weights, and serum
    concentrations of total cholesterol and phospholipids, indicating
    effects on lipid metabolism, at higher doses (Cox et al., 1989).

         Groups of 21 male and 21 female Sprague-Dawley rats were given
    diets containing pyriproxyfen (purity, 97.2%) at concentrations of 0,
    80, 400, 2000, or 10 000 ppm, equal to 0, 4.8, 24, 120, and 680 mg/kg
    bw per day for males and 0, 5.4, 28, 140, and 690 mg/kg bw per day for
    females, for 26 weeks. The observations included clinical signs,
    deaths, food and water consumption, body weight, ophthalmological,
    clinical chemical, haematological, and urinary parameters, organ
    weights, and gross and histological appearance. The serum activities
    of aspartate and alanine aminotransferases, alkaline phosphatase,
    lactate dehydrogenase, leucine aminopeptidase, creatine phosphokinase,
    and gamma-glutamyl transpeptidase were measured. Blood samples were
    taken at the end of the study.

         There were no deaths, and the only signs of toxicity were
    increased incidences of alopecia around the neck and soft stools
    during the early stage of the study in animals at 10 000 ppm. The body
    weights of animals at 10 000 ppm were significantly decreased
    throughout the study, by 86% in males and 87% in females at the end of
    study. Marked decreases in body-weight gain were observed at this
    dose. There were no treatment-related changes in food or water
    consumption. Proteinuria and increased urinary excretion of potassium
    ion were observed in animals at 10 000 ppm. Slight but significant
    decreases in erythrocyte count and haematocrit were observed in males
    at 2000 and 10 000 ppm and in females at 10 000 ppm. The haemoglobin
    concentration was also slightly but significantly decreased at this
    dose. No increase in platelet count was observed. Slight but
    significant increases in total protein, albumin, and blood urea
    nitrogen were observed in animals at 10 000 ppm. The albumin and
    a2u-globulin fractions were slightly but significantly increased in
    males at 10 000 ppm. Total cholesterol and phospholipid concentrations
    were significantly increased in males at 2000 and 10 000 ppm and in
    females at 10 000 ppm. Of the serum enzyme activities studied, only
    that of  gamma-glutamyl transpeptidase was significantly increased in
    males at 10 000 ppm. Significantly increased absolute weights of the
    liver were observed in animals at 10 000 ppm (130% of control value in
    males and in females), and significant increases in the relative
    weight were observed in males at doses > 2000 (110% at 2000 ppm and
    160% of control values at 10 000 ppm) and in females at 10 000 ppm

    (100% at 2000 ppm and 150% of control values at 10 000 ppm).
    Significantly increased relative kidney weights were observed in
    animals at 10 000 ppm, but the absolute weights were not significantly
    increased. Histopathological examination showed slight hypertrophy of
    the liver in all animals at 10 000 ppm. The NOAEL was 400 ppm, equal
    to 24 mg/kg bw per day, on the basis of increased relative liver
    weight, increased total cholesterol and phospholipid concentrations
    indicating effects on lipid metabolism, and mild anaemia at higher
    doses (Koyama et al., 1989).

         Groups of five male and five female Sprague-Dawley (Crl:CD) rats
    received dermal applications of pyriproxyfen (purity, 97.2%) dissolved
    in corn oil at doses of 0, 100, 300, or 1000 mg/kg bw per day under a
    semi-occlusive dressing for 6 h/day for 21 days. The observations
    included clinical signs, deaths, food consumption, body weight, and
    clinical chemical, haematological, and and histological examinations.
    Serum was assayed for alanine and aspartate aminotransferases. Blood
    samples were collected at termination. The study complied with GLP.

         There were no treatment-related effects on the mortality rate,
    clinical signs, or haematological or clinical chemical parameters,
    including serum enzymes. There were no significant changes in body
    weight or food consumption in the treated group, and no effect of
    treatment on organ weights was observed. Histopathological examination
    revealed no treatment-related alterations in the liver or any other
    tissues examined. The NOAEL was 1000 mg/kg bw per day, the highest
    dose tested (Moore et al., 1993).

         Groups of 10 male and 10 female Sprague-Dawley (Jcl:CD) rats were
    exposed to a mist aerosol of pyriproxyfen dissolved in corn oil at
    concentrations of 270, 480, or 1000 mg/m3 for 4 h/day for 28 days.
    The mass median aerodynamic diameter of the particles was 0.71-0.88
    m. The observations included clinical signs, deaths, food and water
    consumption, body weight, and urinary, ophthalmological, clinical
    chemical, haematological, and histological examinations. Serum was
    assayed for leucine aminopeptidase, cholinesterase, lactate
    dehydrogenase, creatine phosphokinase, alanine and aspartate
    aminotransferase, and alkaline phosphatase activity. Blood samples
    were collected at termination after a 16-h fast. The study complied
    with GLP.

         There were no deaths. Salivation was observed early in the study
    in rats at the highest concentration, and the body-weight gain of
    animals at this dose was sporadically, slightly but significantly
    lower, although it was normal at the end of the study. There were no
    treatment-related changes in food consumption or in haematological,
    urinary, or ophthalmologic parameters. Slightly but significantly
    increased lactate dehydrogenase activity was observed in males at the
    highest dose, but the activities of the other serum enzymes showed no
    treatment-related change. A slight but significant increase (9%) was
    observed in the relative weight of the liver at 1000 mg/m3, but the
    absolute weight was comparable to that of controls. Histopathological
    examination revealed no treatment-related morphological changes in the

    organs of exposed rats. The NOAEL was 480 mg/m3 on the basis of
    salivation, sporadically reduced body-weight gain, and increased
    lactate dehydrogenase activity at 1000 mg/m3 (Kawaguchi et al.,
    1988).

          Guinea-pigs 

         The skin sensitizing potential of pyriproxyfen (purity, 97.2%)
    was tested in a GLP-compliant study in male Hartley guinea-pigs by the
    maximization method. A volume of 0.05 ml of 1% pyriproxyfen in
    Freund's complete adjuvant mixed with water or a 0.5% solution of
    pyriproxyfen in corn oil was injected intradermally for initial
    sensitization. As a challenge, 0.2 g of pyriproxyfen in 25% petrolatum
    or 0.2 ml of a positive control was applied dermally in patches to
    test animals for 24 h, 6 days after the first sensitization. No dermal
    reaction was observed (Suzuki et al., 1987f).

          Rabbits 

         New Zealand white rabbits of each sex received a single dose of
    0.5 g of pyriproxyfen (purity, 97.2%) as a fine powder moistened with
    physiological saline by dermal application for 4 h. The potential to
    induce primary skin irritation was examined 4.5, 24, 48, and 72 h
    after application. The study complied with GLP. No oedema or erythema
    was observed (Suzuki et al., 1987g).

         A single dose of 100 mg of pyriproxyfen (purity, 97.2%) in a
    volume of 0.1 ml was applied to the right eye of three male and three
    female New Zealand white rabbits in a study that complied with GLP.
    The potential to induce primary eye irritation was examined 1, 24, 48,
    and 72 h after application in unwashed eyes. Slight conjunctival
    redness (grade 1) and chemosis (grade 1-2) were observed in all
    treated animals 1 h after application. Conjunctival redness (grade 1),
    chemosis (grade 1), and discharge (grade 2) were still apparent in one
    or two animals after 24 h, but these changes had disappeared by 48 h
    after application. Pyriproxyfen was considered to be a minimal ocular
    irritant (Suzuki et al., 1987g).

          Dogs 

         Groups of four male and four female beagle dogs, 6 months old,
    received gelatine capsules containing pyriproxyfen (purity, 97.2%) at
    doses of 0, 100, 300, or 1000 mg/kg bw per day for 3 months. The
    observations included clinical signs, deaths, food consumption, body
    weight, and ophthalmic, electrocardiographic, clinical chemical,
    haematological, urinary, and histological parameters. The activities
    of alkaline phosphatase, aspartate and alanine aminotransferases,
    gamma-glutamyl transpeptidase, creatine phosphokinase, and lactate
    dehydrogenase were measured in plasma. Ophthalmological examinations
    were performed during weeks 0, 5, and 12 of treatment, and an
    electrocardiograph was obtained at the same times. Blood samples were
    collected during weeks 0, 4, 8, and 12 of treatment; hepatic function
    was assessed by bromsulphalein retention during weeks 0, 6, and 13 of

    treatment, and renal function was assessed by retention of
     para-aminohippuric acid during weeks 0, 5, and 11 of treatment.

         No deaths were observed. Female dogs at 1000 mg/kg bw per day had
    a slightly increased incidence of soft stools, but no other
    treatment-related toxic signs were observed. There were no changes in
    body weight, body-weight gain, food consumption, or ophthalmological
    parameters throughout the study, and no treatment-related changes in
    the electrocardiograph were observed at any dose. Haematological
    parameters were not significantly changed at any dose, although
    slight, nonsignificant alterations in the number of platelets (by
    < 39%) and total cholesterol concentration (by < 67%) were observed,
    with no obvious dose-dependence. The phospholipid concentration was
    significantly increased in females at 1000 mg/kg bw per day. No
    significant changes was found in the activities of the serum enzymes
    studied, although there were trends to increased alkaline phosphatase
    activity in males at the high dose, lactate dehydrogenase activity in
    males at all doses and in females at the high dose, and creatine
    phosphokinase activity in males in all doses, with no dose-dependence.
    Aspartate and alanine aminotransferase activities were unaltered.
    Hepatic function was not significantly affected at any dose. The
    absolute weights of the liver were significantly increased in males at
    300 and 1000 mg/kg bw per day, by 30% and 26%, respectively, and
    significant increases in relative liver weights were observed in males
    at 300 mg/kg bw per day, by 24%. Increased incidences of
    hepatocellular hypertrophy were observed in females at 300 mg/kg bw
    per day and in animals of each sex at 1000 mg/kg bw (0/4 in controls,
    0/4 at 100 mg/kg bw per day, 0/4 at 300 mg/kg bw per day, and 4/4 at
    1000 mg/kg bw per day in males, and 0/4, 0/4, 3/4, and 4/4 in females,
    respectively). At 1000 mg/kg bw per day, increased incidences of
    eosinophilic bodies in the liver were observed (0/4 in controls, 0/4
    at 100 mg/kg bw per day, 0/4 at 300 mg/kg bw per day, and 2/4 at 1000
    mg/kg bw per day in males, and 0/4, 0/4, 0/4, and 2/4 in females,
    respectively). Electron microscopic examination revealed a minimal to
    slight increase in smooth endoplasmic reticulum with slight dilatation
    in the livers of all animals at 1000 mg/kg bw per day. These changes
    are consistent with adaptation of the liver to exposure to the
    compound through enzyme induction. A slight but significantly
    prolonged retention ratio in the test for renal function was observed
    in males at 300 and 1000 mg/kg bw per day after 6 weeks of treatment,
    but the retention ratio was normal by the end of the study, and no
    treatment related histopathological changes were observed in the
    kidney. The NOAEL was 100 mg/kg bw per day on the basis of increased
    absolute and relative liver weights and an increased incidence of
    hepatocellular hypertrophy at higher doses (Nakano et al., 1988).

         Groups of four male and four female beagle dogs (23-27 weeks old)
    were given gelatine capsules containing pyriproxyfen (purity, 95.3%)
    at doses of 0, 30, 100, 300, or 1000 mg/kg bw per day for 52 weeks.
    The observations included clinical signs, deaths, food consumption,
    body weight, and ophthalmoscopic, clinical chemical, haematological,
    urinary, and histological examinations. The activities of alanine and
    aspartate aminotransferases, alkaline phosphatase, and creatine

    phosphokinase were measured in plasma. Blood samples were collected 1
    week before and on weeks 12, 24, 37, and 50 of treatment. The study
    conformed to GLP.

         Two males at 1000 mg/kg bw per day were killed  in extremis with
    acute weight loss and, in one case, liver failure, at weeks 17 and 31
    of treatment. Slightly increased frequencies of salivation and
    diarrhoea were observed in animals at 1000 mg/kg bw per day, and
    emaciation was observed in males at doses > 300 mg/kg bw per day.
    There were no treatment-related ophthalmological abnormalities. A
    dose-dependent but nonsignificant reduction in body weight was seen
    throughout the study, and body-weight gains were significantly reduced
    in animals at doses > 300 mg/kg bw per day. Food consumption was
    not reduced at any dose. Significant changes were seen in several
    haematological parameters, including 10-20% decreases in haemoglobin
    and erythrocyte counts and a slightly but significantly increased mean
    corpuscular volume in males at doses > 300 mg/kg bw per day and in
    females at doses > 100 mg/kg bw per day and a significantly
    decreased packed cell volume in the latter group. The change in
    haemoglobin in males at 1000 mg/kg bw per day was not significant.
    These haematological changes might indicate slight anaemia. There was
    no abnormality of cellularity or cell composition in the bone marrow.
    Statistically significant decreases in the number of lymphocytes were
    observed in all treated females at weeks 12 and 37, which were
    attributed to transiently high values for the control group. The
    platelet count was significantly increased in males at doses > 100
    mg/kg bw per day and females at 1000 mg/kg bw per day throughout the
    study. Slightly but significantly prolonged prothrombin times were
    observed in males at 300 mg/kg bw per day and in animals of each sex
    at 1000 mg/kg bw per day. Significantly increased plasma enzyme
    activities were seen, including those of alkaline phosphatase in
    animals at doses > 300 mg/kg bw per day throughout the study,
    alanine aminotransferase in animals at 1000 mg/kg bw per day
    throughout the study, and aspartate aminotransferase in males at 1000
    mg/kg bw per day in weeks 12, 24, and 37 of treatment. The total
    cholesterol concentration in plasma was significantly increased in
    animals at doses > 30 mg/kg bw per day (by 24-58% at 30 mg/kg bw
    per day, 64-160% at 100 mg/kg bw per day, 100-140% at 300 mg/kg bw per
    day, and 76-100% at 1000 mg/kg bw per day) throughout the study, and
    the plasma concentrations of triglycerides were significantly
    increased in animals at doses > 100 mg/kg bw per day. These
    increases were dose-dependent except at the highest dose in males, but
    in this group there were only two survivors. No reduction in plasma
    protein fractions was observed in the treated groups.

         A slightly reduced pH and increased volume of urine were observed
    in males at 1000 mg/kg bw per day throughout the study. The absolute
    weights of the liver were dose-dependently increased in all treated
    groups and significantly increased in males at doses > 100 mg/kg bw
    per day (by 130% at 30 mg/kg bw per day, 150% at 100 mg/kg bw per day,
    170% at 300 mg/kg bw per day, and 190% of control values at 1000 mg/kg
    bw per day) and in females at doses > 300 mg/kg bw per day (110%,
    120%, 140%, and 140%, respectively). The relative weights of the liver

    were significantly increased in males at doses > 30 mg/kg bw per
    day (130% of control value) and in females at doses > 300 mg/kg bw
    per day. The absolute weights of the thyroid were significantly
    increased in females at doses > 300 mg/kg bw per day, and the
    relative weights were significantly increased in females at doses
    > 100 mg/kg bw per day. Significantly increased relative renal
    weights were observed in males at 300 mg/kg bw per day and in females
    at doses > 300 mg/kg bw per day; the absolute weights were
    dose-dependently but not significantly increased.

         Macroscopic examination showed enlarged livers and hepatic damage
    in the two dogs at 1000 mg/kg bw per day which died. Histopathological
    examination revealed treatment-related hepatic damage in animals of
    each sex at 1000 mg/kg bw per day, which was characterized by
    centriacinar fibrosis in 2/2 males and 3/4 females and bile-duct
    hyperplasia in 2/2 males and 3/4 females; foci of cystic degeneration
    in 1/2 males and 1/4 females; active chronic inflammation in 2/2 males
    and 2/4 females; and nodular hyperplasia in 2/2 males and 0/4 females.
    Submucosal fibrosis in the gall-bladder was observed in all male
    animals, including those that had died, and in 3/4 females at 1000
    mg/kg bw per day, in association with bile-duct hyperplasia. One of
    four males at 30 mg/kg bw per day had focal bile-duct hyperplasia and
    focal subcapsular fibrosis, but these effects were not observed at 100
    or 300 mg/kg bw per day. There were no preneoplastic or neoplastic
    alterations. Although no morphological alterations were seen in the
    liver, the increase in cholesterol concentration and relative liver
    weight at low doses might be related to treatment. No NOAEL could be
    identified, as increased total cholesterol concentrations indicating
    effects on lipid metabolism and increased relative liver weights with
    a trend towards increased absolute liver weights were seen at all
    doses (Chapman et al., 1991).

         In a complementary study which complied with GLP, groups of four
    male and four female beagle dogs (19-24 weeks old) were given gelatine
    capsules containing pyriproxyfen (purity, 95.3%) at doses of 0, 3, or
    10 mg/kg bw per day for 52 weeks. The observations included clinical
    signs, deaths, food consumption, body weight, and ophthalmic, clinical
    chemical, haematological, urinary, and histological examinations. The
    activities of alanine and aspartate aminotransferases, alkaline
    phosphatase, and creatine phosphokinase were assayed in serum. Blood
    samples were collected after 12, 24, 36, and 50 weeks of treatment.

         There were no deaths, signs of clinical toxicity, or changes in
    body weight, body-weight gain, or food consumption. Significantly
    increased platelet counts were observed in males at 3 mg/kg bw per day
    in weeks 24, 36, and 50 of treatment and in those at 10 mg/kg bw per
    day in week 36, but with no clear dose-dependence. Prothrombin time
    was not prolonged in males at any dose. Females at 10 mg/kg bw per day
    also showed significantly increased platelet counts in weeks 36 and 50
    (by 8% at 3 mg/kg bw per day and 10% at 10 mg/kg bw per day), and
    prothrombin time was slightly but significantly prolonged at these
    doses at the end of study. There were no other treatment-related
    changes in haematological parameters. The total cholesterol

    concentration was unchanged; slight but significant increases in total
    triglyceride concentrations in males at 10 mg/kg bw per day were seen
    in weeks 12 and 36 of treatment. There were no treatment-related
    changes in urinary parameters. The absolute weight of the liver was
    slightly increased in females at 10 mg/kg bw per day (110% of
    control), but this was not significant. No histopathological changes
    were found in any organ, including the liver and kidney. The range of
    mean total platelet counts in controls in other studies in this
    laboratory was 273-357 in males and 305-357 in females, whereas those
    in the present study were 341-367 in controls, 414-462 at the low
    dose, and 415-456 at the high dose in males, and 321-384 in controls
    and 430-478 at the high dose in females. The increased numbers of
    platelets and the prolonged prothrombin time were therefore
    treatment-related changes although no significant increase in platelet
    counts was observed in animals at 30 mg/kg bw per day in the previous
    study (Mitchel et al., 1993).

         The NOAEL for the two 52-week studies in dogs was 10 mg/kg bw per
    day, on the basis of the absence of treatment-related toxicity at 10
    mg/kg bw per day in the second study and changes in lipid metabolism
    and increased liver weight at 30 mg/kg bw per day in the first study.

    (c)  Long-term studies of toxicity and carcinogenicity

          Mice 

         Groups of 60 male and 60 female ICR(Crj-CD-1) mice were given
    diets containing pyriproxyfen (purity, 95.3%; 97.6-98.7% dietary
    concentration) at concentrations of 0, 120, 600, or 3000 ppm for
    78 weeks, providing doses equal to 0, 16, 81, and 420 mg/kg bw per day
    for males and 0, 21, 110, and 530 mg/kg bw per day for females. The
    observations included clinical signs, deaths, food consumption, body
    weight, organ weights, and ophthalmological, haematological, and gross
    and histological examinations. Ten mice from each group were killed
    during week 52 for interim examination, and the surviving mice were
    killed during week 78. Blood samples were taken from 10 rats per group
    during weeks 52 and 78 of treatment. No clinical chemical tests were
    conducted. The study complied with GLP.

         The mortality rate was dose-dependent and significantly increased
    in males at 600 and 3000 ppm (43% at 0 ppm, 55% at 120 ppm, 72% at 600
    ppm, and 82% at 3000 ppm) and in females at 3000 ppm (39% at 0 ppm,
    44% at 120 ppm, 55% at 600 ppm, and 64% at 3000 ppm). There were
    slight, nonsignificant increases in the incidence of clinical signs,
    including reduced motor activity and hunched position, in animals at
    3000 ppm. Statistically significant decreases in body weights,
    body-weight gains, and/or food consumption were observed in males at
    3000 ppm during the study. The absolute and relative weights of the
    liver were significantly increased in females at 3000 ppm during week
    52 of treatment. The haematological parameters showed no
    treatment-related change. Histopathological examination of animals
    that died revealed a significantly increased incidence of systemic
    amyloidosis in the glandular stomach of males at 600 and 3000 ppm and

    the adrenal, thyroid, heart, liver, kidney, glandular stomach, and
    duodenum of females at 3000 ppm, and a dose-related relationship was
    found between the generalized amyloidosis and the mortality rate.
    Statistical analysis of the incidence of graded amyloidosis revealed a
    significant positive trend in renal amyloidosis in females and a
    significant positive trend in hepatic amyloidosis in animals of each
    sex at 3000 ppm. Females at this dose had a significant increase in
    the incidence of lymphocytic infiltration in the liver (22/59 at 0 and
    34/60 at 3000 ppm) and of tubular mineralization (3/59 at 0 and 46/60
    at 3000 ppm). Deposition of amyloid in the kidney causes numerous
    pathological changes including tubular mineralization and papillary
    necrosis. In this study, however, the incidences of tubular
    mineralization and segmental cortical atrophy were increased
    independently of amyloidosis in female animals at 3000 ppm, suggesting
    that the chronic nephrosis was directly related to treatment.
    Histopathological examination revealed no increase in the incidence of
    neoplastic lesions at any dose. The NOAEL was 120 ppm, equal to 16
    mg/kg bw per day, on the basis of increased mortality at higher doses
    (Osheroff et al., 1991a; Cardy et al., 1994).

          Rats 

         Groups of 50 male and 50 female Sprague-Dawley (Crl:CD) rats were
    given diets containing pyriproxyfen (purity, 95.3%) at concentrations
    of 0, 120, 600, or 3000 ppm, equal to 0, 5.4, 27, and 140 mg/kg bw per
    day for males and 0, 7.0, 35, and 180 mg/kg bw per day for females,
    for 104 weeks. Satellite groups of 30 males and 30 females were also
    treated orally. The observations included clinical signs, deaths, food
    and water consumption, body weight, organ weights, and
    ophthalmoscopic, clinical chemical, haematological, urinary, and gross
    and histopathological examination. Assays were performed for the serum
    enzymes aspartate and alanine aminotransferase, alkaline phosphatase,
    creatine kinase, and gamma-glutamyl transpeptidase. Blood samples were
    collected from satellite groups of rats on week 13, 26, 52, 78, and
    104 of treatment. The study complied with GLP.

         Treatment did not affect mortality (34-46% in males and 32-58% in
    females), clinical signs, or ophthalmoscopic end-points. The body
    weights of males were significantly reduced in weeks 13, 26, and 50 of
    treatment (by 5-7%) and those of females in weeks 13, 26, 50, and 78
    of treatment (by 12-14%) at 3000 ppm, but they had returned to the
    control level by the end of study. The mean body-weight gain was
    significantly reduced in females at 600 ppm and in animals of each sex
    at 3000 ppm throughout the study. No treatment-related changes in food
    consumption were observed. The only alteration in haematological
    parameters was a transient increase in eosinophils. Alkaline
    phosphatase activity was significantly increased in males at doses
    > 120 ppm in weeks 26, 52, and 78 of treatment, but the activity
    (87-104 U/L) remained within the range of historical controls (45-114
    U/L), and the changes were not clearly dose-dependent. gamma-Glutamyl
    transpeptidase activity was significantly increased in males at 3000
    ppm in week 104 of treatment and in females at 600 and 3000 ppm in
    weeks 26 and 52. The activities of other serum enzymes were not

    significantly affected. Significantly increased total cholesterol
    concentrations were observed in males at 3000 ppm in weeks 26 and 52
    (149% and 147% of control, respectively). Slight, inconsistent,
    nonsignificant increases in urinary protein concentration were
    observed in females at 3000 ppm in week 26. At interim necroscopy, the
    absolute weights of the liver were found to be nonsignificantly
    increased at week 52 of treatment with 3000 ppm (by 15% in males and
    13% in females). A significant increase in relative liver weight was
    observed only in females at 3000 ppm (120% of control). The only
    significant or treatment-related increases in the incidence of
    morphological alterations at 104 weeks seen on gross and
    histopathological examination were hyperkeratosis of the skin of males
    at 3000 ppm, which was considered not to be biologically significant,
    and a significant increase in the incidence of liver necrosis in males
    at 3000 ppm that died during the study; however, no liver necrosis was
    observed in the surviving males at 3000 ppm at the end of the study,
    indicating nthat it was not related to treatment. Histopathological
    examination revealed no evidence of neoplastic alterations. The NOAEL
    was 600 ppm, equal to 27 mg/kg bw per day, on the basis of reductions
    in body weight and mean body-weight gain and increased absolute and
    relative liver weights at higher doses (Osheroff et al., 1994a,b).

    (d)  Genotoxicity

         The results of tests for the genotoxicity of pyriproxyfen are
    summarized in Table 2. All of the positive controls used in the assays
    produced the expected positive responses. In assays for reverse
    mutation, no induction of revertant colonies was observed at six doses
    with or without an exogenous metabolic activation system (S9). In
    tests for DNA repair, pyriproxyfen was inactive at six doses with or
    without S9. In tests for gene mutation in mammalian cells, no
    mutations were observed at four doses ranging from 10 to 300 ppm
    without S9 or 10 to 100 ppm with S9. In assays for unscheduled DNA
    repair synthesis, pyriproxyfen was cytotoxic and/or inhibited normal
    DNA synthesis but it did not induce unscheduled DNA synthesis. In
    tests for cytogeneticity, Chinese hamster ovary cells (CHOK1) were
    exposed to pyriproxyfen at a concentration of 10, 30, or 100 g/ml for
    2 h in the presence of S9 and cultured for a further 16 or 22 h or
    cultured with pyriproxyfen for 18 or 24 h in the absence of S9.
    Although marked cytotoxicty, characterized by decreased mitotic index
    and cell cycle delay, were observed at doses > 30 mg/ml without S9,
    and at 100 mg/ml with S9, no increase in the total number of
    structural aberrations or the frequency of cells with aberrations was
    observed at any concentration. In the test for micronucleus formation
    in mice  in vivo, a single dose of pyriproxyfen at 5000 mg/kg bw
    slightly but not statistically significantly increased the incidence
    of micronucleated polychromatic erythrocytes.The Meeting concluded
    that pyriproxyfen is not genotoxic  in vivo or  in vitro.


        Table 2. Results of tests for the genotoxicity of pyriproxyfen

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

     In vitro 

    Reverse mutationa    S. typhimurium           10-5000 g/plate          97.2     Negative  S9    Kogiso et al. (1988a)
                         TA98, TA100,
                         TA1537, TA1538,
                         E, coli WP2 uvrA

    DNA repairb          B.subtills M45,          673-21 500 g/disc        95.3     Negative  S9    Kogiso et al. (1992) 
                         H17                      in DMSO

    Gene mutationc       Chinese hamster          3-300 g/ ml              95.3     Negative  S9    Kogiso et al. (1990)
                         V79 cells, hprt locus

    Unscheduled          Human HeLa S3            0.1-205 g/ ml            95.3     Negative  S9    Henderson & 
    DNA synthesisd       epithelioid cells                                                            Proudlock (1989)

    Chromosomal          Chinese hamster          10-300 g/ml              97.2     Negative  S9    Kogiso et al. (1989)
    aberrationse         ovary cells

    Chromosomal          Chinese hamster          9.6-321 g/ml -S9         97.2     Negative  S9    Kogiso et al. (1988)
    aberrationsf         ovary cells              50-200 g/ml +S9

     In vivo 

    Micronucleus         CD-I mice, bone          Single intraperitoneal    95.3     Negative         Proudlock et al. 
    formationg           marrow                   injections of 5000 mg/kg                            (1991)
                                                  bw at 24, 48, and 72 h
                                                                                                                              

    Table 2. (continued)

    All studies were conducted according to good laboratory practice. DMSO, dimethyl sulfoxide
    a  Positive controls were methylmethanesulfonate for TA100, 2-nitrofluorene for TA98 and TA1538, sodium azide for TA1535, 
       ICR-191 for TA1537,  N-ethyl- N'-nitro- N-nitrosoguanidine for WP2 uvrA, benzo[ a]pyrene for TA100, TA98, TA1537, and TA1538 
       and 2-aminoanthracene for TA1535 and WP2 uvrA.
    b  Positive controls were mitomycin C for the direct assay and sterigmatocystin for the activation assay. The negative 
       control was kanamycin in both assays. 
    c  Positive controls were ethylmethane sulfonate for the direct assay and 9,10-dimethyl-1,2-benzanthracene for the activation 
       assay.
    d  Positive controls were 2-acetylaminofluorene for the activation assay and 4-nitroquinoline-1-oxide for the direct assay.
    e  Positive controls were mitomycin C for the direct assay and cyclophosphamide for the activation assay.
    f  Positive controls were mitomycin C for the direct assay and benzo[ a]pyrene for the activation assay. 
    g  Positive control was mitomycin C.
    

    (e)  Reproductive toxicity

         (i)  Multigeneration reproductive toxicity

          Rats 

         Groups of 26 male and 26 female Sprague-Dawley (Crj) rats were
    given diets containing technical-grade pyriproxyfen (purity, 95.3%) at
    concentrations of 0, 200, 1000, or 5000 ppm. The F0 animals were
    treated for 70 days before mating and then for 6 subsequent weeks for
    males and during 3 weeks of gestation and 3 weeks of the lactation
    period for females. The F1 generation were treated for 18 weeks from
    the day of their weaning to the day of weaning of the F2 generation,
    including 77-90 days before mating and the mating, gestation, and
    lactation periods. The mean daily intakes of pyriproxyfen were 14, 68,
    and 340 mg/kg bw per day in males and 20, 98, and 500 mg/kg bw per day
    in females (18, 87, and 440 mg/kg bw per day before mating, 15, 77,
    and 390 mg/kg bw per day during gestation, and 32, 160, and 830 mg/kg
    bw per day during lactation) in the F0 generation, and 17, 83, and
    440 mg/kg bw per day in males and 21, 110, and 560 mg/kg bw per day in
    females (21, 100, and 550 mg/kg bw per day before mating, 14, 72, and
    380 mg/kg bw per day during gestation, and 28, 160, and 810 mg/kg bw
    per day during lactation) in the F1 generation.

         The observations in parental rats included clinical signs,
    deaths, food consumption, body weight, estrus cycle, and
    histopathological and reproductive parameters which included mating,
    fertility, gestation, and live birth indices. All parental animals
    were killed at the end of weaning, and the reproductive organs, brain,
    pituitary, liver, and kidney were examined histopathologically. The
    organs from the F1 parental animals were weighed. Estrus cycles were
    examined by a smear assay during the 10 days before mating. The
    observations in the F1 and F2 pups included viability, body
    weight, and lactation indices. Developmental indices were not
    examined. Groups of 10 male and 10 female pups were selected randomly
    from 10 litters for necroscopy. One male and one female were selected
    randomly from each F1 litter to provide 26 pairs at each dose to
    serve as parents for the F2 generation. Pups were weighed by sex.
    The study complied with GLP.

         The F0 parent animals showed no treatment-related changes in
    clinical signs, mortality rate, reproductive parameters, or estrus
    cycle. Body weight and body-weight gain were significantly reduced in
    F0 animals at 5000 ppm during the periods of premating, gestation,
    and lactation, and food consumption was significantly reduced in F0
    females at this dose during gestation. No gross or histopathological
    alterations were seen that were related to treatment. The NOAEL for
    F0 parental toxicity was 1000 ppm, equal to 68 mg/kg bw per day, on
    the basis of reductions in body weight and body-weight gain at 5000
    ppm. The NOAEL for reproductive toxicity was 5000 ppm, equal to 340
    mg/kg bw per day, the highest dose tested.

         The F1 parent animals showed no treatment-related changes in
    clinical signs, mortality rate, reproductive parameters, or estrus
    cycles. The body weights of F1 males and F1 females at 5000 ppm
    were significantly reduced, and the terminal body weights of animals
    at this dose were significantly decreased (to 98% at 1000 ppm and 88%
    at 5000 ppm in males and 100% at 1000 ppm and 95% at 5000 ppm in
    females). Body-weight gain was also significantly reduced in F1
    males at 5000 ppm during the premating period. Food consumption was
    significantly reduced at this dose in F1 males during treatment and
    in F1 females during gestation. The absolute weights of the liver
    were significantly increased in F1 adults at 5000 ppm (110% at 1000
    ppm and 110% at 5000 ppm in males and 120% at 5000 ppm in females),
    and the relative weights were significantly increased in males at 1000
    ppm (110% of control) and in animals of each sex at 5000 ppm (130% in
    males and 130% in females). Histopathological examination showed an
    increased incidence of focal clear cells in the liver in males at 5000
    ppm, but this effect is commonly observed in male rats and was
    considered to be unrelated to treatment. Significant increases in
    relative kidney weights were observed in males at 1000 ppm (110% of
    control values) and 5000 ppm (110%), but the absolute weights were not
    significantly increased at any dose. Histopathological examination
    showed an increased incidence of chronic interstitial nephrosis (7/26
    at 0 ppm, 3/26 at 200 ppm, 7/26 at 1000 ppm, and 15/26 at 5000 ppm) in
    males at 5000 ppm and in the incidence of hydronephrosis (1/26 at 0
    ppm and 4/26 at 5000 ppm) in females at this dose; however, these
    increases did not reach statistical significance. No other
    treatment-related morphological lesions were observed. The NOAEL for
    F1 parental toxicity was 1000 ppm, equal to 83 mg/kg bw per day, on
    the basis of decreased body weight, decreased food consumption, and
    increased absolute and relative liver weights at 5000 ppm. No evidence
    of reproductive toxicity was observed. The NOAEL for reproductive
    toxicity was 5000 ppm, equal to 340 mg/kg bw per day, the highest dose
    tested.

         In F1 pups, there was no treatment-related change in clinical
    signs, sex ratio, viability index, or lactation index and no
    significant difference between treated and control groups in body
    weight at birth. Significant reductions in body weight were observed
    in male F1 pups on day 21 and in female F1 pups on days 14 and 21
     post partum at 5000 ppm. The total litter weight was also
    significantly decreased on days 14 and 21  post partum at this dose.
    No treatment-related effects were seen on gross examination. F2 pups
    also showed no treatment-related change in clinical signs, sex ratio,
    viability index, or lactation index. The mean pup weights were
    significantly decreased on days 14 and 21  post partum at 5000 ppm.
    No gross pathological alteration related to treatment was apparent at
    any dose. The NOAEL for developmental toxicity was 1000 ppm, equal to
    98 mg/kg bw per day, on the basis of reduced body weight in F1 and
    F2 pups at 5000 ppm (Robinson et al., 1991).

         In a study of treatment before and during the early stages of
    gestation (segment 1) conducted according to GLP, groups of 24 male
    and 24 female Sprague-Dawley rats were given pyriproxyfen (purity,
    97.2%) dissolved in corn oil by gavage at doses of 0, 100, 300, 500,
    or 1000 mg/kg bw per day for 12 weeks comprising 9 weeks before mating
    and 3 weeks of mating, in males or for at least 3 weeks including 2
    weeks before mating and the mating period and on days 0-7 of gestation
    in females. The observations in parental rats included clinical signs,
    deaths, food consumption, body weight, organ weights, gross
    appearance, and reproductive performance including copulation and
    fertility indices. Clinical examinations were performed twice a day.
    Males were killed at the end of mating, and female animals on day 21
    of gestation.

         Treatment-related deaths occurred in two females at the highest
    dose. Increased incidences of diarrhoea and erythema and swelling of
    the anal region were observed in females at 300 mg/kg bw and in
    animals of each sex at doses > 500 mg/kg bw per day. Dose-dependent
    increases in the incidence of salivation were frequently observed in
    all treated groups, with incidences of 0/24 in controls and 18/24,
    21/24, 24/24, and 24/24 at the four doses respectively, in males, and
    0/24, 1/24, 5/24, 7/24, and 8/24, respectively, in females. Body
    weight was significantly reduced in females at 100 mg/kg bw per day
    during gestation and in animals of each sex at doses > 300 mg/kg bw
    per day throughout the study. Body-weight gain and food consumption
    were also significantly decreased in males at doses > 300 mg/kg bw
    per day throughout the study, but significant decreases were observed
    only during treatment in females. Water consumption was significantly
    increased in males at doses > 100 mg/kg bw per day and in females
    at doses > 300 mg/kg bw per day. The absolute weights of the liver,
    kidney, and adrenal glands were significantly increased and the
    absolute weight of the thymus was significantly decreased in males at
    doses > 300 mg/kg bw per day. In females, the absolute weights of
    the kidney and adrenals were significantly increased at 1000 mg/kg bw
    per day. Enlarged, dark-red livers, pitted, enlarged kidneys, enlarged
    adrenals, and thymus atrophy were observed in males at doses > 300
    mg/kg bw per day, and congested, enlarged livers, enlarged adrenals,
    and atrophy of the spleen and thymus were observed in females at
    1000 mg/kg bw per day. There was no treatment-related change in
    reproductive performance. No NOAEL could be identified for maternal
    toxicity, as reduced body weight during gestation was seen at all
    doses. The NOAEL for reproductive toxicity was 1000 mg/kg bw per day,
    the highest dose tested.

         Slightly but significantly reduced numbers of corpora lutea (90%
    of control) and of live fetuses (88% of control) were observed at 1000
    mg/kg bw per day, but the values were within the range in historical
    controls. Slight increases in placental weight and in fetal body
    weight were observed at 1000 mg/kg bw per day, but the effects were
    not dose-dependent and were within the range in historical controls. A
    slight but significant increase in the number of phalanges of the
    proximal forepaw was observed, but such increases are known to be
    associated with an altered growth rate. The incidences of external,

    visceral, and skeletal anomalies were not increased. The NOAEL for
    developmental toxicity was 1000 mg/kg bw per day, the highest dose
    tested (Saegusa et al., 1988a).

         In a study of treatment during the perinatal and lactation
    periods (segment 3) conducted according to GLP, groups of 23-24
    pregnant Sprague-Dawley rats were given pyriproxyfen (purity, 97.2%)
    dissolved in corn oil by gavage at doses of 0, 30, 100, 300, or 500
    mg/kg bw per day from day 17 of gestation to day 20  post partum. The
    dams were allowed to deliver naturally. On day 4  post partum, the
    offspring were culled to adjust the litter size to eight (four males
    and four females when possible) for tests of development (F1I), and
    the remaining pups (F1II) were killed for skeletal examination on
    the day of culling. The dams (F0) were killed at termination of
    weaning. The observations in maternal rats included clinical signs,
    deaths, body weight, food consumption, organ weights, gross
    appearance, and reproductive indices including delivery rate, birth
    rate, and body weight of live newborns. The F1I offspring were
    weighed on days 0, 4, 7, 14, and 21  post partum during lactation;
    after weaning, one male and one female per litter were weighed once a
    week. Clinical signs were observed twice a day. The indices of
    development during lactation included separation of the auricle,
    emergence of abdominal hair, eruption of incisors, separation of
    eyelids, and descent of testes or opening of the vagina. On day 20,
    all F1 offspring were examined for sensory function in tests for
    visual placing, righting and mid-air righting reflexes, and response
    to pain. On day 21  post partum, two male and two female offspring
    from each litter (F1Ia) were killed for visceral and skeletal
    examination. After weaning, another male and female from each litter
    (F1Ib) were examined for emotionality (behaviour in an open field)
    at 4 weeks of age, for motor coordination (rotarod performance) at 5
    weeks of age, and for learning ability (in a water-filled multiple T
    maze) at 6 weeks of age. The F1Ib offspring were killed for necropsy
    on day 56  post partum. Another male and female from each litter
    (F1Ic) were tested only for reproductive performance after being
    paired for mating within the same group (avoiding sibling matings) at
    11 weeks of age. The fetuses were removed surgically from mated
    females on day 21 of gestation. Reproductive performance was assessed
    from indices of mating, fertility, gestation, and litters. The fetuses
    (F2) were weighed and examined for external anomalies.

         In the F0 maternal animals, treatment-related deaths were
    observed at 500 mg/kg bw per day, an increased incidence of diarrhoea
    at doses > 300 mg/kg bw per day, and dosedependent increases in the
    incidence of salivation at doses > 100 mg/kg bw per day (0/23 in
    controls and 0/23, 1/23, 2/24, and 4/24 at the four doses,
    respectively). During gestation, significantly reduced body weights
    were observed at 500 mg/kg bw per day, and significantly reduced
    body-weight gain and food consumption were seen frequently during the
    study at doses > 300 mg/kg bw per day. The absolute and relative
    weights of the liver were significantly increased at doses > 300
    mg/kg bw per day. Atrophy of the thymus, congestion of the liver and
    kidneys, enlargement of the adrenals, and atrophy of the spleen were

    observed at 500 mg/kg bw per day, and an increased number of
    stillborns was seen at this dose. The body weight of live newborn pups
    was significantly decreased at doses > 300 mg/kg bw per day. The
    NOAEL for maternal toxicity was 100 mg/kg bw per day, on the basis of
    clinical signs, reductions in body weight, body-weight gain, and food
    consumption, and decreased body weight of delivered newborn at 300
    mg/kg bw per day.

         At 500 mg/kg bw per day, the survival rate of F1 offspring was
    significantly decreased on days 0-4  post partum, and the weaning
    rate was decreased on days 4-21  post partum. No decrease in the
    viability of F1I offspring was observed on days 21-77. The body
    weights of pups of each sex at doses > 300 mg/kg bw per day were
    significantly reduced on days 0-49 or 56  post partum. All of the
    physical developmental indices were significantly retarded and slight
    retardation of sexual differentiation was observed at doses > 300
    mg/kg bw per day. No treatment-related change in sensory functions was
    observed in F1I offspring. Visceral examination of the F1Ia
    offspring on day 21  post partum revealed a significant increase in
    the number with anomalies at 30, 300, and 500 mg/kg bw per day (0% in
    controls and 10%, 1.2%, 17.2%, and 29% at the four doses,
    respectively).The anomalies consisted mainly of dilatation of the
    renal pelvis and hyperaemia and/or inflammatory cell infiltration. The
    incidence of dilatation of the renal pelvis was significantly
    increased at doses > 300 mg/kg bw per day (0% in controls and 3.8%,
    1.2%, 14%, and 18% at the four doses, respectively, with 0-3.2% in
    historical controls). The incidence of hyperaemia and/or inflammatory
    cell infiltration was significantly increased at 500 mg/kg bw per day
    (0% in controls and 3.8%, 0%, 5.8%, and 12% at the four doses,
    respectively). Although developmental insufficiency of the papilla or
    stenosis and obstruction of the urethra can cause dilatation of the
    renal pelvis, as can developmental retardation, the range in
    historical controls of this strain was 0-2.0% in fetuses and 0-3.2% in
    21-day-old offspring, and recovery from dilatation of the renal pelvis
    usually occurs after birth. No skeletal anomalies were found that were
    related to treatment. The absolute weights of all organs of F1
    offspring killed on day 21  post partum were slightly but
    significantly decreased, but no treatment-related change was found in
    the absolute weights of the organs of F1Ib offspring killed on day
    56  post partum. The changes in organ weights might have been due to
    retarded physical development. Ambulation was also slightly but
    significantly increased at doses > 100 mg/kg bw per day (by 31% at
    100 mg/kg bw per day, 50% at 300 mg/kg bw per day, and 37% at 500
    mg/kg bw per day). Motor coordination was comparable to that of
    controls, and no treatment-related changes in learning ability were
    observed. All the changes observed in the F1 offspring, including
    increased ambulation, could have been due to retarded physical
    development. After maturation, the reproductive perfomance of F1Ic
    offspring was comparable to that of controls. The body weight and
    body-weight gain of pregnant F1 animals were comparable to those of
    controls during gestation. The NOAEL for developmental toxicity was
    100 mg/kg bw per day, on the basis of decreased body weight,

    retardation of physical development, and visceral anomalies associated
    with the retarded growth rate at 300 mg/kg bw per day.

         Significantly reduced numbers of implantations (12 in controls
    and 10, 12, 11, and 9.2 at the four doses, respectively) and mean
    numbers of live F2 fetuses (12 in controls and 9.3, 11, 10, and 8.5
    at the four doses, respectively) were observed at 500 mg/kg bw per
    day. Significantly reduced numbers of corpora lutea, implantations,
    and live fetuses were found at 30 mg/kg bw per day but not at 100
    mg/kg bw per day. These reductions were not dose-dependent. There were
    no treatment-related differences in fetal body weight or in the
    incidence of external anomalies between treated and control groups.
    The NOAEL for F1 reproductive toxicity was 300 mg/kg bw per day, on
    the basis of a reduction in the number of implantations and in the
    mean number of live fetuses at 500 mg/kg bw per day (Saegusa et al.,
    1988b).

         (ii) Developmental toxicity

          Rats 

         In a study that complied with GLP, groups of 36 female
    Sprague-Dawley rats were given pyriproxyfen (purity, 97.2%) dissolved
    in corn oil by gavage at doses of 0, 100, 300, or 1000 (42 animals)
    mg/kg bw per day on days 7-17 of gestation. The fetuses (F1I) were
    removed surgically from 23 pregnant dams (F0I) at 0, 100, or 300
    mg/kg bw per day and from 20 at 1000 mg/kg bw per day on day 21 of
    gestation and examined for developmental toxicity. The remaining 10-13
    dams (F0II) were allowed to deliver normally. On day 4  post 
     partum, the offspring were culled to adjust the litter size to eight
    (four males and four females when possible) for functional testing on
    day 20  post partum (F1IIa). The remaining pups (F1IIb) were
    killed at 21 days of age and examined for skeletal anomalies. During
    lactation, developmental indices were examined. After weaning, one
    male and one female from each litter (F1IIa1) allocated for
    functional testing were examined for emotionality at 4 weeks of age,
    for motor coordination at 5 weeks of age, and for learning ability at
    6 weeks of age; these offspring were killed for necropsy at 8 weeks of
    age. Another male and female from each litter (F1IIa2) were tested
    for reproductive performance after being paired for mating within the
    same group (avoiding sibling mating) at 11 weeks of age, and the
    fetuses were removed surgically from the mated females on day 21 of
    gestation. The remaining offspring (F1IIa3) were killed for
    necroscopy at 21 days of age, after weaning.

         The observations in parental rats included clinical signs,
    deaths, food and water consumption, body weight, estrus cycle, and
    organ weights. The postnatal developmental indices included separation
    of the auricle, emergence of abdominal hair, eruption of incisors,
    separation of eyelids, and descent of testes or opening of the vagina.
    The sensory function tests included visual placing, righting and
    mid-air righting reflexes, and response to pain. Emotionality was
    evaluated by observation of behaviour in an open field, motor

    coordination was examined in a rotarod performance test, and learning
    ability was examined by behaviour in a water-filled multiple T maze
    test. Reproductive performance included indices of mating, fertility,
    gestation, and litters.

         Of the F0 dams, 12 of 42 at 1000 mg/kg bw per day died between
    day 11 and day 16 of gestation. No deaths occurred in the other
    groups. Signs of toxicity were observed at doses > 300 mg/kg bw per
    day. At the highest dose, these included diarrhoea, erythema and
    swelling of the anal region, hypoactivity, wasting, hypothermia,
    lachrymation, and piloelection. Signs of toxicity were also observed
    at 300 mg/kg bw per day but in only one animal. Body weight and
    body-weight gain were significantly reduced at 300 and 1000 mg/kg bw
    per day during gestation and at 100 mg/kg bw per day during treatment.
    Food consumption was significantly reduced at doses > 100 mg/kg bw
    per day during treatment, and water consumption was dose-dependently
    and significantly increased at doses > 300 mg/kg bw per day. Thymic
    atrophy and enlarged adrenals were observed in the dams that died and
    those killed on day 21 of gestation (F0I) at 1000 mg/kg bw per day.

         In the F0I dams, from which fetuses were removed surgically on
    day 21 of gestation, slight but significant increases were found in
    the relative weights of the liver and kidney at 300 mg/kg bw per day,
    but no significant increase in the absolute weights was observed at
    this dose. At 1000 mg/kg bw per day, the absolute weights of the
    kidney and adrenal were significantly increased and the absolute
    weight of the thymus was significantly decreased. The relative weight
    of the liver was significantly increased, but the absolute weight was
    not significantly affected at 1000 mg/kg bw per day. Higher ratios of
    resorbed or dead fetuses were observed at 1000 mg/kg bw per day (4.7%
    in controls, 7.7% at 300 mg/kg bw per day, and 15% at 1000 mg/kg bw
    per day). None of these differences achieved statistical significance
    or was outside the historical control range (5.7%; 1.5-20%). There was
    no difference in the mean numbers of corpora lutea or implantations or
    the implantation rate. In the F0II dams, body weight and body-weight
    gain were significantly reduced at 300 and 1000 mg/kg bw per day
    during lactation. There were no treatment-related changes in the
    number of live newborn, the length of gestation, or the delivery rate.
    No NOAEL could be identified for F0 maternal toxicity since
    decreased body-weight gain was seen at all doses. The NOAEL for
    reproductive toxicity was 1000 mg/kg bw per day, the highest dose
    tested.

         No significant change in F1I fetal sex ratio, placental weight,
    or fetal body weight was observed, but the ratio of resorbed or dead
    fetuses was increased (5% in controls and 15% at 1000 mg/kg bw per
    day) and the number of live fetuses was decreased at the highest dose,
    but these changes were not statistically significant. Cyclopia and
    polydactyly were each observed in one fetus at 300 mg/kg bw per day
    (0.7%), but not in any other group, and these anomalies were
    considered to be unrelated to treatment. There were no
    treatment-related increases in the incidences of external, visceral,
    or skeletal anomalies. A significant increase in the number of fetuses

    with a skeletal variation consisting of opening of the foramen
    transversarium of the seventh cervical vertebra was seen at 300 and
    1000 mg/kg bw per day (0% in controls and 1.5%, 5.0%, and 14% at the
    three doses, respectively). An increased number of fetuses with an
    extra lumbar rib was observed at 1000 mg/kg bw per day, but this was
    not significant. The NOAEL for developmental toxicity was 300 mg/kg bw
    per day, on the basis of increased skeletal variations at 1000 mg/kg
    bw per day.

         The F1IIa offspring showed no-treatment related effect on
    survival or weaning rates. The body weights of the treated groups were
    comparable to those of controls during lactation and before mating.
    There were no treatment-related effects on postnatal physical
    development, sexual differentiation, sensory function, emotional
    behaviour, or motor coordination. A significant retardation in the
    time taken to reach the goal in the water-filled multiple T maze was
    observed in females at 1000 mg/kg bw per day, but this slight
    reduction in learning behaviour was observed only in the second of
    three consecutive daily trials. There was no impairment of
    reproductive performance of F1IIa2 offspring at any dose. No
    external anomalies were observed in F2 fetuses. The NOAEL for
    developmental toxicity was 1000 mg/kg bw per day, if the slight
    evidence of behavioural teratogenicity in F1 offspring is ignored.

         In the offspring killed at 21 days of age (F1IIb), an increased
    incidence of skeletal variations was observed at 1000 mg/kg bw per day
    (9% in controls and 18% at 1000 mg/kg bw per day), but this was not
    statistically significant. No external or skeletal anomalies were
    observed. The incidence of visceral anomalies was increased
    significantly in F1IIaI offspring at 1000 mg/kg bw per day killed at
    56 days of age (0/46 in controls and 7/39 at 1000 mg/kg bw per day).
    F1IIb and F1IIaI offspring at 1000 mg/kg bw per day also showed an
    increased incidence of dilatation of the renal pelvis. The total
    incidence of dilatation of the renal pelvis observed in F1I
    offspring (killed at 21 and 56 days of age and at the end of the
    fertility test) was increased dose-dependently (0/98 in controls and
    1/95, 3/85, and 9/79 at the three doses, respectively). The incidences
    in controls from 15 previous studies were 0-2.0% in fetuses, 0-3.2% in
    offspring 21 days old, 0-4.3% at 56 days of age, and 0-4.5% at the end
    of the fertility test. The incidence in the controls in the present
    study was 0% at all times. The incidence of protrusion or partial
    adhesion of the liver parenchyma on the diaphragmatic side was also
    increased at 1000 mg/kg bw per day (1/98 in controls and 0/95, 2/85,
    and 6/79 at the three doses, respectively). These anomalies were not
    observed in fetuses removed surgically. The overall NOAEL for
    developmental toxicity was 300 mg/kg bw per day, on the basis of an
    increased incidence of skeletal variations in fetuses and an increased
    incidence of visceral anomalies in offspring at 1000 mg/kg bw per day
    (Saegusa et al., 1988c).

          Rabbits 

         Groups of 15-18 female JW-NIBS rabbits were treated by gavage
    with pyriproxyfen (purity, 97.2%) at doses of 0, 100, 300, or 1000
    mg/kg bw per day on days 6-18 of gestation and were killed on day 28
    of gestation. The study complied with GLP.

         In the maternal animals, abortion or premature delivery occurred
    at doses > 300 mg/kg bw per day, in one control, none at 100 mg/kg
    bw per day, three at 300 mg/kg bw per day, and six at 1000 mg/kg bw
    per day. Dead and moribund animals were found at 1000 mg/kg bw per day
    (none at 0, 100, or 300 mg/kg bw per day and three at 1000 mg/kg bw
    per day). Several signs of toxicity, including soft stools,
    emaciation, decreased spontaneous activity, and bradypnoea were
    observed in aborted, prematurely delivered, prematurely dying, and
    moribund dams at doses > 300 mg/kg bw per day. Body weight,
    body-weight gain, and food consumption were significantly reduced in
    dams at 1000 mg/kg bw per day. There were no significant effects on
    the mean number of corpora lutea or implantations or the number, sex
    ratio, or body weight of live fetuses.

         The live fetuses showed no treatment-related external anomalies.
    Skeletal or visceral malformations were observed in fetuses at 300
    mg/kg bw per day, comprising a defect of the third distal phalanx of
    the hind leg in one; cystic lung, ventricular septal defect,
    hypoplasia of the left atrial auricle, and persistent truncus
    arteriosus in one; and a defect of the gall-bladder in one. None was
    observed in the other groups. External malformations were observed in
    three fetuses, comprising local oedema, a visceral malformation, and
    microphthalmia in one fetus at 300 mg/kg bw per day; persistent
    truncus arteriosus in one fetus at 1000 mg/kg bw per day; and a
    ventricular septal defect in another at this high dose. The total
    incidence of malformations was 1% in controls, 1% at 100 mg/kg bw per
    day, 6% at 300 mg/kg bw per day, and 2% at 1000 mg/kg bw per day. The
    authors concluded that pyriproxyfen did not cause treatment-related
    changes in the incidences of skeletal anomalies, skeletal variations,
    ossification, visceral anomalies, or visceral variations. The NOAEL
    for reproductive toxicity was 100 mg/kg bw per day on the basis of
    abortion or premature delivery and a number of signs of toxicity at
    300 mg/kg bw per day. The NOAEL for developmental toxicity was 1000
    mg/kg bw per day, the highest dose tested (Hirohashi et al., 1988).

    (f) Studies on metabolites

         (i)  Acute toxicity

         The metabolites of pyriproxyfen were administered orally to mice
    in a 0.5% solution of methylcellulose at 1000 or 2000 mg/kg bw. One
    out of five males given 5''-hydroxypyriproxyfen (purity, 97.5%) at
    2000 mg/kg bw died, but no deaths occurred with the other metabolites.
    4'-Hydroxypyriproxyfen (purity, 98.3%) caused no abnormal clinical
    signs; 5''-hydroxypyriproxyfen caused decreased spontaneous activity
    in animals at both doses and ataxic gait at 2000 mg/kg bw;

    4-hydroxyphenyl  (RS)-2-(2-pyridyloxy) propyl ether pyriproxyfen
    (purity, 90.1%) produced decreased spontaneous activity, ataxic gait,
    and prone position in animals at 2000 mg/kg bw;  (RS)-2-hydroxypropyl
    4-phenoxyphenyl ether (purity, 99.0%) produced decreased spontaneous
    activity, ataxic gait, prone position, lateral position, and irregular
    respiration in animals at 2000 mg/kg bw; and  (RS)-2-(2-pyridyloxy)
    propionic acid (purity, 100%) produced decreased spontaneous activity
    at 2000 mg/kg bw (Misaki, 1993a).

         (ii) Genotoxicity

         4'-Hydroxypyriproxyfen (purity, 98.3%), 5''-hydroxypyriproxyfen
    (purity, 97.5%), 4-hydroxyphenyl  (RS)-2-(2-pyridyloxy) propyl ether
    pyriproxyfen (purity, 90.2%),  (RS)-2-hydroxypropyl 4-phenoxyphenyl
    ether (purity, 99.0%), and  (RS)-2-(2-pyridyloxy) propionic acid
    (purity, 100%) were tested for mutagenicity in  Salmonella 
     typhimurium TA98, TA100, TA1535, and TA1537 and in  Escherichia 
     coli WP2  uvrA, with and without exogenous metabolic activation at
    concentrations of 15-5000 g/plate. None of the metabolites caused
    reverse mutation, whereas the positive controls used in these assays
    produced the anticipated responses (Hara et al., 1993).

         No data were available on the effects of the metabolites of
    pyriproxyfen on chromosomal integrity, but as these metabolites are
    formed  in vivo and pyriproxyfen had no effect on this end-point,
    this is not considered a major gap in the data.

    Comments

         After oral administration to rats, [14C]pyriproxyfen is slowly
    (time to peak concentration in plasma, 8 h) and incompletely (< 50%
    of the dose) absorbed but is then rapidly eliminated, predominantly in
    the faeces (90%), with only 4-11% in the urine, after 48 h. Absorbed
    pyriproxyfen is excreted mainly via the bile (34-37% of the
    administered dose in 48 h). The metabolism of pyriproxyfen is
    qualitatively similar in rats, mice, lactating goats, and laying hens.
    A large number of metabolites have been detected, the main route of
    biotransformation being 4'-hydroxylation. Other pathways include
    hydroxylation of the pyridyl ring, ether cleavage and conjugation.
    Mice conjugate a much greater proportion of the dose than rats. The
    concentration of pyriproxyfen in tissues other than fat was very low
    (generally < 0.01 g equivalent per g after 72 h; fat < 0.1g
    equivalent per g). The half-times of the radiolabel in tissues,
    including blood and fat, were 8-36 h. The dermal absorption of
    pyriproxyfen has not been studied.

         The acute oral toxicity of pyriproxyfen is low, with LD50
    values > 5000 mg/kg bw in mice, rats, and dogs. The acute dermal
    toxicity is also low, with LD50 values > 2000 mg/kg bw in mice and
    rats, and after exposure by inhalation, with an LC50 value > 1.3
    mg/l air in mice and rats. WHO (1999) has classified pyriproxyfen as
    'unlikely to present acute hazard in normal use'. Pyriproxyfen was

    mildly irritating to the eye but not to the skin of rabbits. It did
    not sensitize the skin of Hartley guinea-pigs in a maximization test.

         In short- and long-term studies of the effects of pyriproxyfen in
    mice, rats, and dogs, the liver was the main toxicological target,
    with increases in liver weight and changes in plasma lipid
    concentrations, particularly cholesterol, at doses of 120 mg/kg bw per
    day and above in rats. There was some evidence that the compound might
    cause modest anaemia in mice, rats, and dogs at high doses. In mice
    treated with pyriproxyfen in the diet for three months, additional
    effects seen included increased mortality rates, histopathological
    changes in the kidney, and decreased body weight. The NOAEL was 150
    mg/kg bw per day in mice, 23 mg/kg bw per day (two studies) in rats,
    and 100 mg/kg bw per day in dogs fed pyriproxyfen in the diet for 3
    months. In long-term studies of toxicity in mice, pyriproxyfen also
    caused a dose-dependent increase in the occurrence of systemic
    amyloidosis, which was associated with increased mortality rates. The
    NOAEL was 120 ppm, equal to 16 mg/kg bw per day. In rats, the only
    additional effect was reduced body-weight gain, and the NOAEL was 600
    ppm, equal to 27 mg/kg bw per day. In two 1-year studies in dogs,
    pyriproxyfen was administered in capsules. The overall NOAEL was 10
    mg/kg bw per day on the basis of increased relative liver weight and
    increased total plasma cholesterol concentration in males. There was
    some evidence that pyriproxyfen can act as a hepatic enzyme inducer,
    at least in dogs. Pyriproxyfen was not toxic when administered
    dermally to rats for 21 days at doses of up to 1000 mg/kg bw per day.
    Inhalation of pyriproxyfen for 4 h per day for 28 days caused only
    minor effects in rats (initial salivation, sporadically reduced
    body-weight gain, slightly increased serum lactate dehydrogenase
    activity) at 10 000 mg/m3. The NOAEL was 480 mg/m3.

         Pyriproxyfen was not carcinogenic when given in the diet at doses
    up to 420 mg/kg bw per day in a study in mice or at doses up to 140
    mg/kg bw per day in rats. Pyriproxyfen showed no evidence of
    carcinogenicity in a 1-year study in dogs at doses up to 1000 mg/kg bw
    per day. The Meeting concluded that pyriproxyfen does not pose a
    carcinogenic risk to humans.

         Pyriproxyfen was not genotoxic in an adequate range of tests for
    mutagenicity and cytogenicity  in vitro and  in vivo. The Meeting
    concluded that pyriproxyfen is not genotoxic.

         The reproductive toxicity of pyriproxyfen in rats has been
    investigated in a two-generation study of reproductive toxicity, a
    study involving treatment of males and females before and in the early
    stages of gestation (segment 1), and a study of treatment during the
    prenatal and lactation periods (segment 3). The NOAEL for maternal
    toxicity was 1000 ppm, equal to 98 mg/kg bw per day, in the
    two-generation study and 100 mg/kg bw per day in the segment 3 study.
    Reproductive toxicity was observed only in the segment 3 study, in
    which there was an increased number of stillbirths in the F0
    generation and a reduction in the number of implantations and in the
    mean number of live fetuses in the F1 generation at 500 mg/kg bw per

    day. The NOAEL for reproductive toxicity was 300 mg/kg bw per day. No
    reproductive toxicity was observed in the two-generation study, the
    NOAEL being 5000 ppm, equal to 340 mg/kg bw per day, the highest dose
    tested, or in the segment 1 study, the NOAEL being 1000 mg/kg bw per
    day, the highest dose tested.

         The developmental toxicity of pyriproxyfen has been studied in
    rats and rabbits. In rats, a NOAEL for maternal toxicity was not
    identified, as decreased body-weight gain was observed at 100 mg/kg bw
    per day, the lowest dose tested. Pyriproxyfen caused little
    developmental toxicity and was not teratogenic. In a segment 3 study,
    the F1 offspring were subjected to a series of developmental tests
    for possible neurotoxicity, including physical indices, tests of
    behaviour, motor and sensory function, and learning ability. Although
    there were some effects on growth at doses > 300 mg/kg bw per day,
    there was no developmental neurotoxicity at 500 mg/kg bw per day, the
    highest dose tested. Visceral anomalies (dilatation of the renal
    pelvis) were found at doses > 300 mg/kg bw per day. The NOAEL for
    developmental toxicity was 100 mg/kg bw per day, on the basis of
    retarded physical development and visceral anomalies at higher doses.
    In a more conventional study of developmental toxicity in rats, no
    evidence of growth retardation or of developmental neurotoxicity was
    found at doses up to and including 1000 mg/kg bw per day, the highest
    dose tested. There was an increased frequency of skeletal variations
    (opening of the foramen transversalium of the seventh cervical
    vertebra) in fetuses at 300 mg/kg bw per day. The frequency of
    visceral anomalies was significantly increased in F1 offspring some
    weeks after birth. The NOAEL for developmental toxicity was 300 mg/kg
    bw per day, on the basis of an increased frequency of skeletal
    variations with visceral anomalies in F1 offspring at 1000 mg/kg bw
    per day. In a study of developmental toxicity in rabbits, signs of
    maternal toxicity (abortion and premature delivery) were evident at
    doses > 300 mg/kg bw per day (NOAEL, 100 mg/kg bw per day). No
    developmental toxicity was observed, the NOAEL being 1000 mg/kg bw per
    day, the highest dose tested.

         The Meeting established an ADI of 0-0.1 mg/kg bw on the basis of
    the NOAEL of 10 mg/kg bw per day in 1-year studies of toxicity in dogs
    and a safety factor of 100.

         The Meeting concluded that it was not necessary to establish an
    acute reference dose because of the low acute toxicity of
    pyriproxyfen.

    Toxicological evaluation

     Levels that cause no toxic effect 

    Mouse:    120 ppm, equal to 16 mg/kg bw per day (18-month study of
              carcinogenicity)

    Rat:      600 ppm, equal to 27 mg/kg bw per day (2-year study of
              toxicity and carcinogenicity)

              5000 ppm, equal to 345 mg/kg bw per day (reproductive
              toxicity, two-generation study of reproductive toxicity,
              highest dose tested)

              100 mg/kg bw per day (developmental toxicity in a segment 3
              study of developmental toxicity)

    Rabbit:   100 mg/kg bw per day (maternal and reproductive toxicity in
              a study of developmental toxicity)

              1000 mg/kg bw per day (developmental toxicity in a study of
              developmental toxicity, highest dose tested)

    Dog:      10 mg/kg bw per day (1-year study of toxicity)


     Estimate of acceptable daily intake for humans 

         0-0.1 mg/kg bw

     Estimate of acute reference dose 

         Unnecessary

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

         Observations in humans


        Toxicological end-points relevant for setting guidance values for dietary and non-dietary exposure to 
    pyriproxyfen

     Absorption, distribution, excretion, and metabolism in mammals 

    Rate and extent of oral absorption           Slow, incomplete absorption (< 50%), rat
    Dermal absorption                            No data (no systemic toxicity up to 1000 mg/kg bw per day by 
                                                 dermal route, rat)
    Distribution of total residues               Highest concentrations of radiolabel in fat and, to lesser 
                                                 extent, liver, rat
    Potential for accumulation                   Possible limited accumulation in fat, rat
    Rate and extent of excretion                 Rapid, complete, 88-96% within 48 h, primarily in faeces; 
                                                 4-11% in urine, rat
    Metabolism in animals                        Extensive. No parent compound detectable in urine; numerous 
                                                 metabolites: main pathway is 4'-hydroxylation; also hydroxylation 
                                                 of the pyridyl ring, ether cleavage, conjugation, mouse, rat, 
                                                 goat, hen
    Toxicologically significant compounds        Pyriproxyfen
    (animals, plants and environment)

     Acute toxicity 

    LD50, oral                                   > 5000 mg/kg bw, mouse, rat
    LD50, dermal                                 > 2000 mg/kg bw, mouse, rat
    LC50, inhalation                             > 1.3 mg/L, mouse, rat
    Dermal irritation                            Not irritating, rabbit
    Ocular irritation                            Mildly irritating, rabbit
    Dermal sensitization                         Not a sensitizer, guinea-pig

     Short-term toxicity 

    Target/critical effect                       Mouse, rat, dog: liver, increased relative liver weight, mild 
                                                 anaemia, altered lipid metabolism (increased serum cholesterol)
    Lowest relevant oral NOAEL                   13 weeks, rat, 24 mg/kg bw per day
    Lowest relevant dermal NOAEL                 21 days, rat, > 1000 mg/kg bw per day
    Lowest relevant inhalation NOAEL             28-day, rat, > 1.3 mg/L

     Long-term toxicity and carcinogenicity 

    Target/critical effect:                      Mouse, rat, dog: liver, increased liver weight, decreased body 
                                                 weight, altered lipid metabolism (increased plasma cholesterol) 
                                                 (rat, dog)
    Lowest relevant NOAEL                        1 year, dog, 10 mg/kg bw per day (diet)
    Carcinogenicity                              Not carcinogenic, mouse, rat

     Genotoxicity                                 Not genotoxic

     Reproductive toxicity 

    Reproductive target/critical effect          Reduction in number of implantations and live F2 fetuses at F1 
                                                 developmentally toxic dose, rat
    Lowest relevant reproductive NOAEL           345 mg/kg bw per day, rat
    Developmental target/critical effect         Retardation of physical development in F1, rat
    Lowest relevant developmental NOAEL          100 mg/kg bw per day, rat

     Neurotoxicity/Delayed neurotoxicity          No evidence of developmental neurobehavioural toxicity in rat. No 
                                                 evidence of neurotoxicty or neuropathology in medium- or long-term 
                                                 studies in mouse, rat, dog or during development in rat, rabbit

     Other toxicological studies                  Possible enzyme inducer, at least in dogs

     Medical data                                 No data

                                                                                                            
    Summary                      Value                  Study                       Safety factor
                                                                                                            

    ADI                          0-0.1 mg/kg bw         1-year, dog, toxicity       100

    Acute reference dose         Unnecessary
                                                                                                            
    

    References

    Cardy, R., Moore, M., Murphy, B.S., Thakur, A., Tellone, C., Ito, S.,
         Lang, P., Ginevan, M., Driver, J., Stewart, R. & Wilkinson, C.
         (1994) Supplemental data and review of oncogenicity study with
         S-31183 (Sumilarv) in mice (MRID No. 421783-10). Unpublished
         study from Technology Sciences Group Inc. Reference No.
         NNT-41-0116. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Chapman, E.A, Lee, P., Virgo, D.M. & Sparrow, S. (1991) S-31183:
         Toxicity study by oral (capsule) administration to beagle dogs
         for 52 weeks. Unpublished study from Life Science Research Ltd.
         Reference No. NNT-11-0081. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Cox, R.H., Zoetis, T., Cardy, R.H., Alsaker, R.D., Kuhlman, S.M.,
         Lewis, S.A., Thakur, A.K. & Phipps, N.G. (1989) Subchronic
         toxicity Sstudy with S-31183 in rat. Unpublished study from
         Hazleton Laboratories America, Inc. Reference No. NNT-910045.
         Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Cox, R.H., Zoetis, T., Voelker, R.W., Alsaker, R.D., Kuhlman, S.M.,
         Lewis, S.A., Thakur, A.K. & Phipps, N.G. (1990) Subchronic
         toxicity study in mice. Unpublished study from Hazleton
         Laboratories America, Inc. Reference No. NNT-01-0066. Submitted
         to WHO by Sumitomo Chemical Co., Ltd.

    Hara, M., Katoh, H. & Yoshitake, A. (1993a) Reverse mutation test of
         metabolites of pyriproxyfen, 4'-OH-Pyr, 5"-OH-Pyr, DPH-Pyr, POPA
         and PYPAC, in bacterial systems. Unpublished study reference No.
         NNT-30-0104. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Henderson, L.M. & Proudlock, R.J. (1989) Assessment of unscheduled DNA
         repair synthesis in mammalian cells after exposure to S-31183.
         Unpublished study from Huntingdon Research Centre Ltd. Reference
         No. NNT-91-0053. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Hirohashi, A., Kannan, N., Kato, T. & Yamada, H. (1988) Study of
         S-31183 by oral administration during the period of fetal
         organogenesis in rabbits. Unpublished study reference No.
         NNT-80-0033. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Isobe, N., Matsunaga, H., Kimura, K., Yoshitake, A. & Yamada, H.
         (1988a) Metabolism of S31183 in rats. Unpublished study reference
         No. NNM-80-0001. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Isobe, N., Matsunaga, H., Kimura, K., Yoshitake, A. & Yamada, H.
         (1988b) Metabolism of S-31183 in rat (tissue distribution study).
         Unpublished study reference No. NNM-800002. Submitted to WHO by
         Sumitomo Chemical Co., Ltd.

    Kawaguchi, S., Watanabe, T., Suzuki T., Kato, T. & Yamada, H. (1987)
         Acute inhalation toxicity of S-31183 in rats. Unpublished study
         reference No. NNT-70-0022. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Kawaguchi, S., Yoshioka, K., Ito, S., Suzuki, T., Kato, T. & Yamada,
         H. (1988) Subacute inhalation toxicity of S-31183 in rats.
         Unpublished study reference No. NNT-80-0031. Submitted to WHO by
         Sumitomo Chemical Co., Ltd.

    Kogiso, S., Hara, M., Yoshitake, A. & Yamada, H. (1988a) Reverse
         mutation test with S31183 in bacteria systems. Unpublished study
         reference No. NNT-80-0034. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Kogiso, S., Hara, M., Iwawaki, H. & Yamada, H. (1988b) In vitro
         chromosomal aberration test of pyriproxyfen in Chinese hamster
         ovary cells (CHO-K1). Unpublished study reference No.
         NNT-80-0028J. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Kogiso, S., Yamamoto, K., Hara, M., Yoshitake, A. & Yamada, H. (1989)
         In vitro chromosomal aberration test of pyriproxyfen in Chinese
         hamster ovary cells (CHO-K1). Unpublished study reference No.
         NNT-90-0054. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Kogiso, S., Yamada, T., Hara, M., Yoshitake, A. & Yamada, H. (1990) In
         vitro gene mutation test of S-31183 in V79 Chinese hamster cells.
         Unpublished study reference No. NNT-000067. Submitted to WHO by
         Sumitomo Chemical Co., Ltd.

    Kogiso, S. Kato, H. & Nakattuka, S. (1992) Reverse mutation test with
         S-31183 in bacteria systems. Unpublished study reference No.
         NNT-80-0088J. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Koyama, Y., Kimura, J., Yoshioka, K., Watanabe, T., Seki, T.,
         Hosokawa, S., Yamada, H. & Hagiwara, H. (1989) A six-month
         chronic dietary toxicity study of pyriproxyfen in rats.
          J. Toxicol. Sci., 14, 43-64.

    Matsunaga, H., Yoshino, H., Isobe, N., Kaneko, H., Nakatuka, I. &
         Yamada, H. (1995) Metabolism of pyriproxyfen in rats. 1.
         Absorption, disposition, excretion, and biotransformation studies
         with [phenoxyphenyl-14C] pyriproxyfen.  J. Agric. Food Chem., 
         43, 235-240.

    Misaki, Y. & Nakatuka, I. (1993) Acute oral toxicity study of
         pyriproxyphen metabolites, 4'-OH-Pyr, 5"-OH-Pyr, DPH-Pyr, POPA
         and PYPAC in mice. Unpublished study reference No. NNT-30-0107.
         Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Mitchell, D.J., Virgo, D.M., Broadmeadow, A., Chase, K.R., Lee, P. &
         Sparrow, S. (1993) S31183: Toxicity study by oral (capsule)
         administration to beagle dogs for 52 weeks (additional
         investigation). Unpublished study from Life Science Research Ltd.
         Reference No. NNT-31-0102. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Moore, M.R., Zoetis, T., Doyle, D., Cardy, R.H., Pearson, R.C.,
         Walker, M.D., Lewis, S.A., Thomas, D.L., Thakur, A.K., Burlew,
         P.L., Hatcher, C.F. & Vegarra, M. (1993) 21-day dermal toxicity
         study in rats with S-31183. Unpublished study from Hazleton
         Washington, Inc. Reference No. NNT-31-0094. Submitted to WHO by
         Sumitomo Chemical Co., Ltd.

    Nakano, M., Yamamoto, T., Kato, T. & Miyamoto, J. (1986) Acute oral
         toxicity study of S31183 in dogs. Unpublished study reference No.
         NNT-60-0012. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Nakano, M., Kohda, A., Kato, T. & Yamada, H. (1988) Three-month oral
         toxicity study of S31183 in dogs. Unpublished study reference No.
         NNT-80-0037. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Osheroff, M.R., Ziegler, K.A., Cardy, R.H., Alsaker, R.D., Kuhlman,
         S.M., Lewis, S.A., Thakur, A.K., Burlew, P.L. & Nasca, A.J.
         (1991a) Oncogenicity study in mice with S31183. Unpublished study
         from Hazleton Laboratories America, Inc. Reference No.
         NNT-11-0084. Submitted to WHO by Sumitomo Chemical Co.

    Osheroff, M.R., Ziegler, K.A., Machotka, S., Alsaker, R.D., Kuhlman,
         S.M., Lewis, S.A., Thakur, A.K., Burlew, P.L., Devis, P.J. &
         Graham, R. (1991b) Combined chronic toxicity and oncogenicity
         study in rats with S-31183. Unpublished study from Hazleton
         Washington, Inc. Reference No. NNT-11-0085. Submitted to WHO by
         Sumitomo Chemical Co., Ltd.

    Panthani, A.M., Walsh, K.J. & Turck, P. (1996a) Metabolism of
         [phenoxyphenyl-14C]S71639 (pyriproxyfen) in lactating goats.
         Unpublished study from Ricerca, Inc. Reference No. NNM-0043.
         Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Panthani, A.M., Walsh, K.J. & Turck, P. (1996b) Metabolism of
         [pyridyl-14C]S-7 1639 (pyriproxyfen) in lactating goats.
         Unpublished study from Ricerca, Inc. Reference No. NNM-0046.
         Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Panthani, A.M., DiFrancesco, P. & Savides, M.C. (1996c) Metabolism of
         [phenoxyphenyl14C]S-71639 (pyriproxyfen) in laying hens.
         Unpublished study from Ricerca, Inc. Reference No. NNM-0045.
         Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Panthani, A.M., DiFrancesco, P. & Savides, M.C. (1996d) Metabolism of
         [pyridyl-14C]S71639 (pyriproxyfen) in laying hens. Unpublished
         study from Ricerca, Inc. Reference No. NNM-0044. Submitted to WHO
         by Sumitomo Chemical Co., Ltd.

    Proudlock, R.J., Haynes, P. & Goodenough, A.J. (1991) Mouse
         micronucleus test on S31183. Unpublished study from Huntingdon
         Research Centre Ltd. Reference No. NNT11-0082. Submitted to WHO
         by Sumitomo Chemical Co., Ltd.

    Robinson, K., Washer, G. & Noveroske, J. (1991) A dietary 2-generation
         (1 litter) reproduction study of S-31183 in the rat. Unpublished
         study from Bio-Research Laboratories Ltd. Reference No.
         NNT-11-0087. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Saegusa, T., Kitajima, S. & Narama, I. (1988a) Study on administration
         of a test substance prior to and in the early stages of pregnancy
         in rats. Unpublished study from Hamamatsu, Seigiken Research Co.,
         Ltd. Reference No. NNT-80-0036. Submitted to WHO by Sumitomo
         Chemical Co., Ltd.

    Saegusa, T., Kitajima, S. & Narama, I. (1988b) Study on administration
         of S-31183 during the perinatal and lactation periods in rats.
         Unpublished study from Hamamatsu, Seigiken Research Co., Ltd.
         Reference No. NNT-80-0030. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Saegusa, T., Kitajima, S. & Narama, I. (1988c) Study by administration
         of S-31183 during the period of fetal organogenesis in rats.
         Unpublished study from Hamamatsu, Seigiken Research Co., Ltd.
         Reference No. NNT-80-0029. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Suzuki, T., Sako, H., Okuno, Y., Kato, T. & Yamada, H. (1987a) Acute
         oral toxicity of S31183 in mice. Unpublished study reference No.
         NNT-70-0014. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Suzuki, T., Misaki, Y., Okuno, Y., Kato, T. & Miyamoto, J. (1987b)
         Acute oral toxicity of S31183 in rats, Unpublished study
         reference No. NNT-70-0005. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Suzuki, T., Sako, H., Okuno, Y., Kato, T. & Yamada, H. (1987c) Acute
         dermal toxicity of S31183 in mice. Unpublished study reference
         No. NNT-70-0015. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Suzuki, T., Misaki, Y., Okuno, Y., Kato., T. & Miyamoto, J. (1987d)
         Acute dermal toxicity of S-31183 in rats. Unpublished study
         reference No. NNT-70-0006. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Suzuki, T., Kawaguchi, S., Watanabe, T., Kato, T. & Yamada, H. (1987e)
         Acute inhalation toxicity of S-31183 in mice Unpublished study
         reference No. NNT-70-0023. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Suzuki, T., Nakanishi, T., Kato, T. & Miyamoto, J. (1987f) Skin
         sensitization test with S31183 in guinea pigs. Unpublished study
         reference No. NNT-70-0003. Submitted to WHO by Sumitomo Chemical
         Co., Ltd.

    Suzuki, T., Nakanishi, T., Kato, T. & Miyamoto, J. (1987g) Primary eye
         and skin irritation tests with S-31183 in rabbits. Unpublished
         study reference No. NNT-70-000. Submitted to WHO by Sumitomo
         Chemical Co., Ltd.

    WHO (1999)  Recommended Classification of Pesticides by Hazard and 
          Guidelines to Classification 1998-1999 (WHO/PCS/98.21/Rev. 1),
         Geneva, International Programme on Chemical Safety.

    Yoshino, H. (1993a) Metabolism of pyriproxyfen in rat (high-dose,
         14C-concentrations in tissues). Unpublished study reference No.
         NNM-30-0028. Submitted to WHO by Sumitomo Chemical Co., Ltd.

    Yoshino, H. (1993b) Metabolism study of
         (pyridyl-2,6-14C)pyriproxyfen in rat (pyridyl14C-labeled test
         compound, single oral administration at low- and high-doses).
         Unpublished study reference No. NNM-30-0025. Submitted to WHO by
         Sumitomo Chemical Co., Ltd.

    Yoshino, H., Kaneko, H., Nakatsuka, I. & Yamada, H. (1995) Metabolism
         of pyriproxyfen. 2. Comparison of in vivo metabolism between rats
         and mice.  J. Agric. Food Chem., 43, 2681-2686.

    Yoshino, H., Kaneko, H., Nakatsuka, I. & Yamada, H. (1996) Metabolism
         of pyriproxyfen. 3. In vitro metabolism in rats and mice.
          J. Agric. Food Chem., 44, 1578-1581.
    


    See Also:
       Toxicological Abbreviations
       Pyriproxyfen (ICSC)