Ethoxyquin

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Toxicity to Reproduction / Developmental Toxicity: Chronic (3.5 years) study, oral (0, 100, 225 ppm in feed), 2 generation Reproduction / Developmental Toxicity study, dogs (Beagle), m/f: NOAEL(P0,reproduction) = 225 ppm ( ≈5.6 mg/kg bw/d),

NOAEL(P1,reproduction) = 225 ppm (≈5.6 mg/kg bw/d)

Link to relevant study records

Reference

Endpoint:

two-generation reproductive toxicity

Remarks:

also covering developmental parameters

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Remarks:

Peer-reviewed assessment report (attached in section 13)

Guideline:

other: Guideline not stated

Principles of method if other than guideline:

- Principle of test: Reproduction effects of ethoxyquin were investigated in two-generation study in dogs via feed
- Short description of test conditions: In the first mating (F0), groups of five males and 10 females were fed diets containing ethoxyquin at a mean analytical concentration of 0, 100 or 225 ppm for a minimum of 82 days before pairing. The eight male and 13 female pups used subsequently for the F1 matings received diets containing 0, 100 or 225 ppm ethoxyquin from weaning until breeding at an age of 10 - 30 months (2nd estrus cycle in females). Animals were observed and underwent extensive physical examinations routinely
- Parameters analysed / observed: Semen samples were taken during the first week of treatment and around the time of mating in order to determine the volume, sperm count, motility, velocity, and morphology. Urine and blood samples were taken for haematology, clinical chemistry and urinalysis from fasted adults before treatment and at the end of the F0 phase; at weeks 10, 23, 36, 49 and 62 and at termination in the F1 growth phase; and at termination of the F1 mating phase. Ophthalmological examinations were performed at the beginning and end of the F1 growth and mating phases. Mating, whelping, and lactation indices were determined. All F1 adults and pups that showed signs of toxicity were necropsied. A range of tissues from controls and F1 adults at the high dose were examined histologically, with selected tissues from F2 pups that showed clinical signs; the livers and gall-bladders from F1 adults at the low dose and the adrenals and spleens from F1 adult females at the low dose were also examined. Macroscopic and microscopic examinations were performed only on F0 and F1 animals that died or were sacrificed prematurely.

GLP compliance:

no

Remarks:

Although Assessment report date was later, the actual study was performed prior to GLP implementation.

Limit test:

no

Justification for study design:

Dogs were chosen as ethoxyquin is added to commercial dog food to help prevent oxidative deterioration.

Species:

other: dog

Strain:

other: Beagle

Details on species / strain selection:

Dogs were chosen as ethoxyquin is added to commercial dog food to help prevent oxidative deterioration.

Sex:

male/female

Details on test animals or test system and environmental conditions:

no further details given

Route of administration:

oral: feed

Vehicle:

not specified

Details on exposure:

DIET PREPARATION
Diets contain 0, 100 or 225 ppm ethoxyquin.

Details on mating procedure:

Groups of five males and 10 females were fed diets containing ethoxyquin for a minimum of 82 days before pairing.
The eight male and 13 female pups used subsequently for the F1 matings received diets containing 0, 100 or 225 ppm ethoxyquin from weaning until breeding at an age of 10 - 30 months (2nd estrus cycle in females).

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

Groups of five males and 10 females were fed diets containing ethoxyquin for a minimum of 82 days before pairing.
The eight male and 13 female pups used subsequently for the F1 matings received diets containing 0, 100 or 225 ppm ethoxyquin from weaning until breeding at an age of 10 - 30 months (2nd estrus cycle in females).

Frequency of treatment:

continuous in feed

Dose / conc.:

0 ppm (nominal)

Remarks:

control

Dose / conc.:

100 ppm (nominal)

Remarks:

approx. 2.5 mg/kg bw per day

Dose / conc.:

225 ppm (nominal)

Remarks:

approx. 5.6 mg/kg bw per day

No. of animals per sex per dose:

F0: five males and 10 females
F1: eight male and 13 female pups

Control animals:

yes, plain diet

Positive control:

not required

Parental animals: Observations and examinations:

Animals were observed and underwent extensive physical examinations routinely; if possible, they were also observed during labour. Semen samples were taken during the first week of treatment and around the time of mating in order to determine the volume, sperm count, motility, velocity, and morphology. Urine and blood samples were taken for haematology, clinical chemistry and urinalysis from fasted adults before treatment and at the end of the F0 phase; at weeks 10, 23, 36, 49 and 62 and at termination in the F1 growth phase; and at termination of the F1 mating phase. Ophthalmological examinations were performed at the beginning and end of the F1 growth and mating phases. Mating, whelping, and lactation indices were determined. All F1 adults and pups that showed signs of toxicity were necropsied. A range of tissues from controls and F1 adults at the high dose were examined histologically, with selected tissues from F2 pups that showed clinical signs; the livers and gall-bladders from F1 adults at the low dose and the adrenals and spleens from F1 adult females at the low dose were also examined. Macroscopic and microscopic examinations were performed only on F0 and F1 animals that died or were sacrificed prematurely.

Sperm parameters (parental animals):

F0 Semen samples were taken during the first week of treatment and around the time of mating in order to determine the volume, sperm count, motility, velocity, and morphology.

Litter observations:

Animals were observed and underwent extensive physical examinations routinely; if possible, they were also observed during labour. Semen samples were taken during the first week of treatment and around the time of mating in order to determine the volume, sperm count, motility, velocity, and morphology. Urine and blood samples were taken for haematology, clinical chemistry and urinalysis from fasted adults before treatment and at the end of the F0 phase; at weeks 10, 23, 36, 49 and 62 and at termination in the F1 growth phase; and at termination of the F1 mating phase. Ophthalmological examinations were performed at the beginning and end of the F1 growth and mating phases. Mating, whelping, and lactation indices were determined. All F1 adults and pups that showed signs of toxicity were necropsied. A range of tissues from controls and F1 adults at the high dose were examined histologically, with selected tissues from F2 pups that showed clinical signs; the livers and gall-bladders from F1 adults at the low dose and the adrenals and spleens from F1 adult females at the low dose were also examined. Macroscopic and microscopic examinations were performed only on F0 and F1 animals that died or were sacrificed prematurely.

Postmortem examinations (parental animals):

All F1 adults and pups that showed signs of toxicity were necropsied. A range of tissues from controls and F1 adults at the high dose were examined histologically, with selected tissues from F2 pups that showed clinical signs; the livers and gall-bladders from F1 adults at the low dose and the adrenals and spleens from F1 adult females at the low dose were also examined. Macroscopic and microscopic examinations were performed only on F0 and F1 animals that died or were sacrificed prematurely.

Postmortem examinations (offspring):

All F1 adults and pups that showed signs of toxicity were necropsied. A range of tissues from controls and F1 adults at the high dose were examined histologically, with selected tissues from F2 pups that showed clinical signs; the livers and gall-bladders from F1 adults at the low dose and the adrenals and spleens from F1 adult females at the low dose were also examined. Macroscopic and microscopic examinations were performed only on F0 and F1 animals that died or were sacrificed prematurely.

Clinical signs:

not specified

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

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

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

In males, food consumption was reduced during most of the study.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not specified

Haematological findings:

no effects observed

Description (incidence and severity):

There was also an indication of reductions in monocytes and partial thromboplastin times in animals of each sex at the high dose, although all of the values were claimed to be within the normal ranges.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Statistically significant increases in serum alkaline phosphatase activity were seen in male parents at the high dose and in female parents at the low and high dose.

Urinalysis findings:

no effects observed

Description (incidence and severity):

There were no effects on urinary parameters.

Behaviour (functional findings):

not specified

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not specified

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

effects observed, non-treatment-related

Description (incidence and severity):

Two females in the high dose group did not give birth although they were confirmed to be pregnant. There were no other differences between the groups in mating performance, labour, birth, or weaning indices, semen parameters, or clinical signs. Litter size, pup survival, and pup weight and growth were similar in all groups.
Remating of three female controls and two at 225 ppm from this phase which failed to mate during the initial phase was successful.

Key result

Dose descriptor:

NOAEL

Effect level:

>= 5.6 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

reproductive performance

Key result

Critical effects observed:

no

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

At 225 ppm, there was an increased number of pups of each sex with a raw or red anus, dehydration, nasal discharge, and excessive lachrymation. The incidence of the two latter signs was also increased at 100 ppm.
Clinical signs in the surviving animals included excessive lachrymation, dehydration, thinness, and pale gums and showed a dose-related increase in both the number of animals of each sex that were affected and the number of occasions on which a particular sign was observed.
In adults (mating), the only treatment-related clinical sign was excessive lachrymation, which occurred more frequently in males at the low and high doses than in controls.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Among F1 animals, one male at the low dose and two females at the high dose died or were sacrificed in extremis. The male was prematurely killed because of suspected neurological signs; one of the females died of suspected heart disease, and the other was sacrificed because of pneumonia.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

High dose males had a lower mean body weight than controls up to study week 48.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

Initially, animals receiving the high dose consumed more food than controls but subsequently food consumption in this group was consistently lower in weeks 8 - 18 in males and in weeks 8 - 30 in females.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not specified

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

Considerable variations in haematological end-points were seen throughout the study in both treated and control animals. There was evidence of treatment-related effects on erythrocyte count, haematocrit, and haemoglobin, which were reduced by up to 11 % relative to controls in treated males and females at weeks 10 and 23, and on partial thromboplastin times which were reduced in females at the high dose in weeks 23 and 36 and in females at the low dose in weeks 23 and 62 and at the final analysis.
In the F1 mating, Haematological end-points were similar in all groups.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Increased serum activities of alkaline phosphatase, gamma-GT, and alanine aminotransferase and reduced albumin:globulin ratios were found in animals at the high dose in weeks 10, 23 and 36, with evidence of less perturbations at the lower dose. These changes are indicative of impaired liver function.
In the F1 mating, Dose-related changes were seen in a number of clinical chemical parameters in females, which attained statistical significance (p < 0.05) at the high dose. These comprised reductions in glucose, cholesterol, protein, albumin, and albumin:globulin ratio, and increases in total bilirubin concentration and in gamma-GT, alkaline phosphatase, and alanine aminotransferase activities. In males, the dose-related increases in alkaline phosphatase, gamma-GT, and alanine aminotransferase activities did not attain statistical significance.

Urinalysis findings:

no effects observed

Description (incidence and severity):

The results of urinary analysis were unremarkable.

Behaviour (functional findings):

not specified

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Increases in the absolute weights of the spleen and testes and in the weights of these organs (see below) relative to the brain weight were seen in treated males giving statistically significant increases in relation to body weight. In females, increases in the absolute and relative weights of the liver (10 %), kidneys (10 %), and spleen (40 %) were reported but were not statistically significant.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Macroscopic examination showed dark plum-coloured livers in one male and two females at the high dose and cervical lymph node haemorrhages in two females at the low and high doses; these lesions were possibly related to treatment as they were not present in control animals.

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Histopathological examination showed that the liver, pituitary, and spleen were the target organs. The macroscopic finding of increased cervical lymph node haemorrhage in females was not confirmed. A dark-reddish-brown pigment, subsequently identified as protoporphyrin IX, was not found in the livers of controls or males at the low dose but was present in the livers of 7/13 females at the low dose, 2/7 males at the high dose, and 10/11 females at the high dose, with a dose-related increase in severity. The frequencies of fibrosis and haemorrhage of the spleen were increased in females at the high dose (3/11 versus 0/13 in controls), and the incidence of pituitary cysts was increased in animals at the high dose when compared with controls (2/6 versus 0/8 in males and 4/10 versus 2/12 in females)

Histopathological findings: neoplastic:

not specified

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not specified

Reproductive performance:

no effects observed

Description (incidence and severity):

In the F1 mating, there were no clear differences in semen analyses or mating, gestation, whelping, or weaning indices between control and ethoxyquin-treated animals.

Key result

Dose descriptor:

NOAEL

Effect level:

>= 5.6 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

reproductive performance

Key result

Critical effects observed:

no

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

At 225 ppm, there was an increased number of pups of each sex with a raw or red anus, dehydration, nasal discharge, and excessive lachrymation. The incidence of the two latter signs was also increased at 100 ppm.
Clinical signs in the surviving animals included excessive lachrymation, dehydration, thinness, and pale gums and showed a dose-related increase in both the number of animals of each sex that were affected and the number of occasions on which a particular sign was observed.

Dermal irritation (if dermal study):

not examined

Mortality / viability:

mortality observed, non-treatment-related

Description (incidence and severity):

Among F1 animals, one male at the low dose and two females at the high dose died or were sacrificed in extremis. The male was prematurely killed because of suspected neurological signs; one of the females died of suspected heart disease, and the other was sacrificed because of pneumonia.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

High dose males had a lower mean body weight than controls up to study week 48.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

Initially, animals receiving the high dose consumed more food than controls but subsequently food consumption in this group was consistently lower in weeks 8 - 18 in males and in weeks 8 - 30 in females.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not specified

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

Considerable variations in haematological end-points were seen throughout the study in both treated and control animals. There was evidence of treatment-related effects on erythrocyte count, haematocrit, and haemoglobin, which were reduced by up to 11 % relative to controls in treated males and females at weeks 10 and 23, and on partial thromboplastin times which were reduced in females at the high dose in weeks 23 and 36 and in females at the low dose in weeks 23 and 62 and at the final analysis.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Increased serum activities of alkaline phosphatase, gamma-GT, and alanine aminotransferase and reduced albumin:globulin ratios were found in animals at the high dose in weeks 10, 23 and 36 with evidence of less perturbations at the lower dose. These changes are indicative of impaired liver function.

Urinalysis findings:

no effects observed

Description (incidence and severity):

The results of urinary analysis were unremarkable.

Sexual maturation:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Histopathological findings:

not specified

Behaviour (functional findings):

not specified

Developmental immunotoxicity:

not specified

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Treated male pups had increased incidences of grey or pale gums, excessive lachrymation, and dehydration, and female pups had an increased incidence of dehydration.

Dermal irritation (if dermal study):

not examined

Mortality / viability:

mortality observed, non-treatment-related

Description (incidence and severity):

An increased mortality rate in pups at the low dose was not confirmed at the high dose and was probably related to the larger litter sizes in this group; the rates of mortality were 7/62 controls, 24/91 at the low dose, and 10/77 at the high dose.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

The pup weights at birth and to week 6 of gestation were slightly reduced (< 10 %), with a dose-related effect in female pups.

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Sexual maturation:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Histopathological findings:

not specified

Behaviour (functional findings):

effects observed, non-treatment-related

Description (incidence and severity):

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

Developmental immunotoxicity:

not examined

Key result

Dose descriptor:

NOAEL

Generation:

F2

Effect level:

100 ppm (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Critical effects observed:

not specified

Key result

Reproductive effects observed:

no

Estimation of the actual intakes of ethoxyquin in this study was confounded by up to twofold increased consumption during lactation and the fact that 180 and 360 ppm had to be added to obtain nominal concentrations of 150 and 300 ppm, however, the analysis showed mean initial values of 100 and 225 ppm. Although the actual amounts of food consumed varied during the study, a value of 25 g/kg bw per day was considered to be a representative mean, which resulted in intakes of 2.5 mg/kg bw per day ethxyquin at 100 ppm and 5.6 mg/kg bw per day at 225 ppm.

Conclusions:

As information was provided via a peer-reviewed assessment report, it can be considered as sufficiently reliable to assess the reproductive toxicity of ethoxyquin towards dogs.
The results of this study show that ethoxyquin in the diet at concentrations up to 225 ppm did not affect reproductive performance or outcome in beagles. There was no clear overall NOAEL for parental toxicity because of increased incidences of clinical signs such as excess lachrymation and dehydration, clinical chemical changes and pigment deposition in the liver. Because these findings were observed in the F0 and F1 generations as well, the lowest dose, 100 ppm, equal to 2.5 mg/kg bw per day, was considered to be the minimal effect level for both, parental and offspring development. Adverse effects on reproductive performance were not observed, either at the low or at the high dose level. Accordingly, the top dose of 5.6 mg/kg bw/day is considered the NOAEL for reproduction toxicity.

Executive summary:

Reproduction effects of ethoxyquin were investigated in a two-generation study in dogs. In this study, reproduction was not altered at the upper dose level of 225 ppm corresponding to a mean daily intake of 5.6 mg/kg bw. Accordingly, the reproductive NOAEL can be set at (or even above) 5.6 mg/kg bw/day. In contrast, there was no clear overall NOAEL for parental toxicity in that study because of increased incidences of clinical signs such as excess lachrymation and dehydration, clinical chemical changes and pigment deposition in the liver that were still seen at the lowest dose of 100 ppm, equal to 2.5 mg/kg bw per day. Adult dogs in both the F0 and F1 generations were affected. Thus, this dose was considered the LOAEL for parental and offspring toxicity as well.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

5.6 mg/kg bw/day

Study duration:

chronic

Species:

dog

Quality of whole database:

The database is of highest quality, available study was assessed with Klimisch 2, and there is no indication that the absence of toxic effects on reproduction and development is not relevant for humans.

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Effects on developmental toxicity

Description of key information

Toxicity to Reproduction / Developmental Toxicity: Chronic study, oral (0, 100, 225 ppm in feed), 2 generation Reproduction / Developmental Toxicity study, dogs (Beagle), m/f: NOAEL(F1, F2, development) = 225 ppm (≈5.6 mg/kg bw/d)

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
An additional developmental toxicity study does not need to be conducted, as all relevant observations were made in a chronic study on reproduction and development in dogs. Test animals were dosed throughout the study, i.e. also during developmentally critical phases of pregnancy. Ethoxyquin did not interfere with growth or reproductive performance of beagle dogs when fed in the diet at target levels of 100 and 225 ppm through two consecutive generations over 3.5 years. No increases in malformations or variations were observed in pups whose parents were fed ethoxyquin. A few pups in both treated groups exhibited nervous system dysfunction which was attributed to inheritance of an autosomal recessive trait in the breeding colony and was not related to ethoxyquin treatment.
So, this endpoint can be considered as covered, no additional studies need to be conducted, and ethoxyquin does not need to be classified as a developmental toxicant.

Reason / purpose for cross-reference:

reference to other assay used for intermediate effect derivation

Species:

other: n.a.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

5.6 mg/kg bw/day

Study duration:

chronic

Species:

dog

Quality of whole database:

The database is of highest quality, available study was assessed with Klimisch 2, and there is no indication that the absence of toxic effects on reproduction and development is not relevant for humans.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Mode of Action Analysis / Human Relevance Framework

As there were no effects on reproductive performance or development seen in the available chronic 2 generation study in dogs, no conclusions on a possible mode of action and its relevance for humans can be drawn. Dogs are the common non-rodent model organism for humans, so it can be reasonably expected that the absence of effects is also relevant for humans.

Justification for classification or non-classification

There were no effects on reproductive performance or development seen in the available chronic 2 generation study in dogs, so no classification is triggered.