2-methylhydroquinone

Endpoint summary

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Effects on fertility

Description of key information

Since the data on Methylhydroquinone requested by this OECD Guideline could not found in the published literature (MEDLINE, EMBASE) for the targeted substance, and the conduction of respective animal studies is not desirable, reference substances have been selected for evaluation of the toxicity to reproduction.

The selection of reference substances of Methylhydroquinone is justified by the use of Structure-Activity Relationships (QSAR) approaches used as elements in QSAR Toolbox. Regarding substituted phenols, e.g. hydroquinone, p-methyl phenol (p-cresol) and m-hydroxy phenol, similarities and differences in developmental effects were also demonstrated in separate publications. It was demonstrated for example, that maternal and developmental toxicological potencies of such substances may differ. The hydroxyl groups of the selected reference sub-stances, there number and position at the phenol ring determine the principal toxicological activity of the substance, i.e. liver toxicity, although the position of methyl groups at the ring structure may influence the possibility to interact with receptors or enzymes.

Different sources of information on developmental toxicity of reference substances were considered:

1. Published experimental studies

2. Assessment reports of different mostly international committees on the selected reference substances.

Reference substance: Resorcinol (CAS-No.: 108-46-3)

Based on a guideline conform two generation reproductive toxicity study of resorcinol admin-istered via drinking water to rats, the following data are available:

The NOAEL of 3000 mg/l Resorcinol in the in the volume of consumed drinking water correspond to the oral exposition to resorcinol in mg/kg/bw./day:

When expressed on a body weight basis (average of F0 and F1 animals), the highest dose cor-responded to approximately 233 mg/kg body weight per day for males over the entire genera-tion, 304 mg/kg body weight per day for females during premating and gestation, and 660 mg/kg body weight per day for females during lactation.

Consequently, the NOAEL for toxicity to reproduction and developmental toxicity for the reference substance Resorcinol is equal to 233 mg/kg body weight per day for males over the entire generation, 304 mg/kg body weight per day for females during premating and gestation, and 660 mg/kg body weight per day for females during lactation.

Reference substance: Hydroquinone (CAS-No.: 123-31-9)

Developmental toxicity study with Hydroxyquinone in rats (1992):

The NOAEL for maternal and developmental toxicity in rats was estimated as 100 mg/kg/day in rats.

A two-generation reproduction study with Hydroquinone in rats (1993):

The NOAEL for reproductive and developmental toxicity in rats was specified to150 mg/kg/day

A study of developmental toxicity with Hydroquinone in rabbit (1992)

The NOAEL for maternal toxicity was 25 mg/kg/day in rabbits.

The NOAEL for developmental toxicity was 75 mg/kg/day in rabbits.

Reference substance Methylresorcinol (CAS-No.: 608-25-3)

The authors of a guideline conform subchronic, teratological and dominant lethal study of 2-methylresorcinol in rats did not specify a NOAEL for reproductive toxicity. However, one can suggest that the NOAEL is > 1345 mg/kg/daily for rats under the study conditions.

An expert panel concluded based on the same study a NOAEL for 2-methylresorcinol in rats for teratogenicity and embryotoxicity of 900 mg/kg/day. However NOAEL of 400 mg/kg/day was estimated based on early unpublished studies in rats.

Reference substance: Cresols (o-, m-, p- and m/p mixture)

A current assessment on the effects of p-cresol on fertility and development in rats (max. 450 mg/kg/d) and rabbits (max. 100 mg/kg/d) (feed studies) concluded: The available, well-conducted two-generation and developmental toxicity studies with p-cresol administered to rats and rabbits provide sufficient information to conclude that the registered substance does not have a specific effect on reproductive toxicity.(EU_REACH 2016)

Nevertheless, a former quoted in the NTP technical report on a 13 week toxicity studies of cresols in rats (max 30,000 ppm) revealed no changes in dosed males, but a lengthening of the oestrus cycle was observed for dosed females. There were no histopathological changes in the ovary or uterus.

Link to relevant study records

Reference

Reference 1

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

HYPOTHESIS FOR THE ANALOGUE APPROACH
Common functional group(s) and common mechanism(s) of action.

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Version / remarks:

March 22, 1996

Deviations:

no

GLP compliance:

yes

Limit test:

no

Specific details on test material used for the study:

Yellow powder, melting point 170,9 ℃
Purity 98,8%
Storage conditions: 4, 6 to 7.0 ° C, dark, under nitrogen
Supplier:

Species:

rat

Strain:

Crj: CD(SD)

Details on species / strain selection:

Source
Charles River Japan Co., Ltd. (Atsugi Production Center)
Number of purchased animals
52 males, 62 females

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST animals:
number: 48 male, 58 female
age: 9 weeks
weight at starting administration:
male: 297 to 368 g,
female: 190 to 230 g

Diet:
Radio-sterilized solid feed for experimental animals (CRF-1, Oriental Yeast Co., Ltd.), ad libitum
Water: ad libitum

Acclimation period: 1 week

Identification of anmimals: labelled on tails, after grouping by ear punching

Environmental conditions
Temperature
21.4 to 22.2 ° C (tolerance range 19.0 to 25.0 ° C)
21.2 to 23.3 ° C (tolerance range 19.0 to 25.0 ° C)
Relative Humidity
49.4 to 64.3% (tolerance range 35.0 to 75.0%)
44.9 to 61.1% (tolerance range 35.0 to 75.0%)
Ventilation
6 to 20 times / hour, fresh air supply
Photoperiod:
12 hours / day (7: 00-19: 00)

Cage
(1) Period excluding the whole period of male and female pregnancy / nursing period
Stainless steel hanging wire mesh cages (195W × 325D × 180H mm), exchanged once within 15 days.
(2) pregnancy / nursing period
Using a polycarbonate cage (265 W × 426 D × 200 H mm), exchanged once within 7 days.

Route of administration:

oral: gavage

Vehicle:

other: (0.5 w / v% CMC-Na containing 0.1 w / v% Tween 80)

Details on exposure:

female:
14 days before mating, mating period, gestation period and 4 days of nursing through delivery (day of delivery = nursing day 0)
male:
14 days before mating, and a total of 42 days from the mating period to the day before necropsy.
A recovery period of 14 days after the end of the administration period was given to 5 males and 5 females in the control and in 300 mg / kg group.

Details on mating procedure:

mating period up to 14 days

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

By HPLC method for each dose. The average value of each concentration is within the set concentration ± 10%, C.V. value is within 10% (upper layer, middle layer, lower layer) of the sample. Set concentration of each administration solution is 95.8 to 98.7%, C.V. value is 0.5 to 0.6% (see Attachment 12.4).

Duration of treatment / exposure:

Male
A total of 42 days were taken from 14 days before mating and through the mating period to the day before necropsy.
Female:
42 - 56 days
Pregnant and lactating animals
14 days before mating, mating period, gestational period, and 4 days of lactation through parturition day. (Day 0) However, females who did not mate were kept until the day before necropsy.
Females who did not copulate were treated to the day before necropsy.

Frequency of treatment:

once a day between 8:28 and 12:16.

Details on study schedule:

Start of test December 9, 2005
Start of experiment December 14th, 2005
Animal arrival December 14, 2005
Administration December 22, 2005 - February 15, 2006
Mating period starting January 5 th, 2006
Parturition January 28th to February 11th 2006
Nursing 4 day until neonatal dissection February 1, 2006 to February 15, 2006
Male dissection after the administration period February 2nd, 2006

Dose / conc.:

0 mg/kg bw/day

Remarks:

recovery

Dose / conc.:

10 mg/kg bw/day

Dose / conc.:

60 mg/kg bw/day

Dose / conc.:

300 mg/kg bw/day

Dose / conc.:

300 mg/kg bw/day

Remarks:

recovery

No. of animals per sex per dose:

12 per sex per dose

Control animals:

yes

Positive control:

no

Parental animals: Observations and examinations:

behaviour,
body weight, food consumption,
hematology, blood biochemistry,
male urinanalysis,
Organ weight
pathological examination (anatomic alterations, histopathology

Oestrous cyclicity (parental animals):

cytological examination

Sperm parameters (parental animals):

histopathological examination of testis and epididymis

Litter observations:

number of birth, presence of sex and outer abnormalities, body weight,

Postmortem examinations (parental animals):

yes

Postmortem examinations (offspring):

no

Statistics:

yes

Reproductive indices:

gestation index, number of corpora lutea, number of implantation sites, number of pups

Offspring viability indices:

number of living pups on day 4

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Salivation (300 mg/kg bw), Irregular respiration (300 mg/kg bw),
Decrease in locomotor activity (300 mg/kg bw), Tonic convulsion (agonal stage), Clonic
convulsion (agonal stage)

Mortality:

mortality observed, treatment-related

Description (incidence):

300 mg/kg bw
Male death 3 of 12
Female 7 of 12

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

M, F slightly decreasing 300 mg/kg bw

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

M, F slightly decreasing 300 mg/kg bw
In the 300 mg / kg group, no statistically significant difference was found. However, in female experimental animals, the tendency to low levels was noted from the 14th to the 20th day of gestation.
The female test animals of the 300 mg / kg satellite group showed a significantly high value on the 36th day. But since the change was only temporary, it was considered a coincidence. In the male experimental animals of the 10 mg / kg group and female animals of the 60 mg / kg group no significant differences to the control group were found.

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

not specified

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of the application phase, low levels of red blood cells, hemoglobin concentration and hematocrit, as well as high levels of platelets and reticulocytes, were observed in male animals of the 300 mg / kg group. In addition, low values ​​of red blood cells, hemoglobin concentration, and hematocrit, and a tendency for platelets and reticulocytes to be high, were measured in male animals of the 60 mg / kg group. Further, there was a tendency for high levels of leukocytes in both male and female experimental animals of the 300 mg / kg group. At the end of the regeneration phase, low erythrocyte values ​​and high levels of reticulocytes were measured in male animals of the 300 mg / kg group. In addition, a low value of mean corpuscular hemoglobin concentration and a longer thromboplastin time were measured in female experimental animals of the 300 mg / kg group. However, since the difference was marginal and no change in male experimental animals of the same group could be detected at the end of the application phase, this is considered a coincidence.
In male animals of the 10 mg / kg group and in female animals of the 10 and 60 mg / kg group no significant difference to the control group was found.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

After the end of the application phase, a high level of total bilirubin was measured in female experimental animals of the 300 mg / kg group. In addition, although a high level of ALP activity was measured in female animals of the 60 mg / kg group, no difference was found in the 300 mg / kg group and no compound was found, therefore this is considered a coincidence. Although the study at the end of the regeneration phase found a high A / G ratio in female animals of the 300 mg / kg group, no difference was found in the study after the end of the application period in male experimental animals, so this was considered as coincidence.

Urinalysis findings:

no effects observed

Description (incidence and severity):

Male: Protein, glucose, Ketone body, Bilirubin, Urobilinogen were tested

Behaviour (functional findings):

no effects observed

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In the planned autopsy of the experimental animals changes in the spleen and the liver were found in both male and female experimental animals, which suggest a effect of the test substance.
In 1 male test animal of the 60 mg / kg group, in 5 male and 4 female experimental animals of the 300 mg / kg group, respectively after the application phase were autopsied and in 4 male animals of the 300 mg / kg group, according to the Regeneration phase were autopsied, elevated levels of hemosiderin dye were detected in the spleen. Hemosiderin deposits were found in 5 male and 3 female animals of the 300 mg / kg group, respectively, after the application phase, and in 3 male and 4 female animals of the 300 mg / kg group, which were postoperatively post-recovery detected on the Kupffer cells of the liver. In 1 female test animal of the 60 mg / kg group, which was autopsied after the regeneration phase, a subcutaneous tumor was detected. Histologically, it was adenocarcinoma of the mammary gland. In 1 female test animal of the 300 mg / kg group, which was autopsied after the regeneration phase, abnormal lobation of the liver was noted. Histologically, however, it was normal liver tissue. Inflammatory infiltration of the adrenal zona reticularis was detected in 2 female animals of the 300 mg / kg group and 1 female animal of the 10 and 60 mg / kg groups. In addition, various histological changes in dead animals, in experimental animals that were autopsied after the application phase and in experimental animals that were autopsied after the regeneration phase, found. However, these changes occurred unspecifically and since their occurrence was not clearly group-dependent, they are assessed as not dependent on the test substance. Furthermore, no abnormalities were found in the ovaries of non-pregnant animals.

Deceased animals of the 300 mg / kg groups were found to have degenerations of the cardiac muscle 1 case of middle and heavy degree in male animals and 1 case of slight degree in a female animal. In 2 male experimental animals, advanced extramedullary hematopoiesis of erythrocytes in the spleen was found in 2 male 5 female experimental animals increased levels of hemosiderin dye also in the spleen. In 3 male and 1 female experimental animals, some eosinophilic inclusion bodies were detected in liver cells. In 3 female animals slight hemosiderin deposits were detected on the Kupffer cells. In addition, medium-grade erosion in the anterior stomach area was observed in 1 male test animal, slight uterine and vaginal bleeding in 2 female test animals, and inflammatory infiltration of the adrenals zona reticularis in 1 female test animal. In 2 female experimental animals pulmonary edema and in 1 female experimental animal anomalous contents in the stomach and the ileum, but no histological changes, were found. In addition, although changes were detected in the lung, kidney, thyroid and parathyroid glands, these were also detected nonspecifically in the control group and thus suggest that they are not related to the test substance.

In the dam, of which all descendants have died, degeneration of the mid heart muscle, advanced extramedullary hematopoiesis of erythrocytes and eosionophilic inclusion bodies in liver cells has been noted. This corresponded to the findings in other dead animals. In addition, focal necrosis of liver cells, extramedullary hematopoiesis, mammary atrophy, pulmonary edema, blood clots, erosion of the duodenum, inflammatory infiltration of the uterine and vaginal mucosa were noted.
As described, mild to severe degeneration of the heart muscle has been noted in dead animals and in the dam, whose entire offspring have died. However, post-mortems after the application phase were

Histopathological findings: neoplastic:

no effects observed

Reproductive function: oestrous cycle:

effects observed, treatment-related

Description (incidence and severity):

In the study of the oestrus cycle, no change in the average value of the respective groups was found and thus no change that could be attributed to the test substance. Also, there were no experimental animals with abnormal oestrus cycles. As a result of mating, all trial pairs have mated up to 1 trial pair of the 300 mg / kg group. At the mating rate, days to mating, missed estri, as well as conception rate, no significant difference between application group and control group was found.

Reproductive function: sperm measures:

not examined

Reproductive performance:

effects observed, treatment-related

Description (incidence and severity):

In the 300 mg / kg group, from the 15th to the 22nd day of pregnancy, 4 out of 10 experimental animals died and led to a reduction in the birth rate. The deceased animals were examined for number of corpus luteum and implantations. Thus, a implantationrate could be determined, which flowed into evaluation. As a result, low values of corpus luteum could be detected in the same group, indicating a tendency to low levels of implantations and offspring. With gestation time, implantationrate and total birth rate no significant difference could be determined between application group and control group.
Although dying of all offspring of 1 dam of the 300 mg / kg group was observed on day 1 of the nursing phase, no abnormal lactation was observed. In other dams, no abnormal behavior was observed at birth or breastfeeding.

Key result

Dose descriptor:

NOAEL

Effect level:

60 mg/kg bw/day

Based on:

test mat.

Sex:

female

Basis for effect level:

reproductive function (oestrous cycle)

reproductive performance

Key result

Dose descriptor:

NOEL

Effect level:

60 mg/kg bw/day

Based on:

test mat.

Sex:

female

Basis for effect level:

reproductive function (oestrous cycle)

reproductive performance

Clinical signs:

not specified

Mortality / viability:

mortality observed, non-treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

The number of live male offspring 4 days after birth in the 300 mg / kg group was low. Also, a tendency to low levels of total 4-day survival animals and survival was noted. In the general findings, as well as the external examination of the offspring no anomalies could be determined on the basis of the test substance.
Furthermore, a deviation from the control group in the sex distribution was found in the 60 mg / kg group, but since such a deviation could not be detected in the 300 mg / kg group, this is considered a coincidence.
Body weight
See Table 38, Appendices 41, 44!
The body weight could not be significantly different from the control group in either male or female animals.
Autopsy
See Table 40, Appendix 43!
In the autopsy of fourth offspring, non-breastfeeding or cannibalism was sporadically detected in the various groups, but no abnormalities attributable to the test substance.

Key result

Generation:

F1

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other:

Remarks on result:

not measured/tested

Remarks:

acc. to the OECD Guideline 422 derivation of effect levels for F1 is not foreseen and du to the limits of study design not possible.

Key result

Reproductive effects observed:

yes

Lowest effective dose / conc.:

300 mg/kg bw/day

Treatment related:

yes

Relation to other toxic effects:

not specified

Dose response relationship:

yes

Relevant for humans:

not specified

Conclusions:

Since the increase in spleen hemosiderin pigment was observed in the group of 60 mg / kg or higher, in females death and increase in spleen hemosiderin pigment was observed in 300 mg / kg group, NOEL for reproductive and developmental toxicity is considered to be 60 mg/kg/day.
In animals, the birth rate, the low value of the corpus luteum, and the low value for the death of all newborns and the survivability of newborns. It is considered to be 60 mg / kg / day.
NOEL on Reproductive Developmental Toxicity and NOAEL was unchanged in male animals at 300 mg/kg /day, dams and F1 children.
In animals, the birth rate, low number of corpora lutea and low values for all-birth mortality and neonatal survival the NOAEL is considered to be 60 mg/kg.

Executive summary:

4 out of 10 animals in the 300 mg / kg group died during pregnancy (15-22 days gestation) and this resulted in a low birth rate. In addition, 1 female died from the group during the nursing phase. Also, low levels of corpora lutea were noted, and thus a tendency to low levels of implantation and live births. The female experimental animals showed no abnormalities in general findings, body weight or feeding quantity before the mating phase. A negative effect of the test substance on the stated values during ovulation (14-21 days of application) does not seem likely. Therefore, it is assumed that the test substance has caused a reduction of the oocytes (low values of corpora lutea). A reduction of implantations relative to corpora lutea or live births to implantations could not be detected, thus excluding negative impact on implantation or pregnancy. During the nursing phase, 1 case occurred in which offspring of a dam of the 300 mg / kg group died. Normal nursing behavior was observed on the day of birth, but it is believed that at this time the mother already suffered from circulatory problems due to myocardial degeneration, so that it is assumed that the situation thereafter rapidly deteriorated,

resulting in impaired breastfeeding ability and thus death of all descendants resulted. Further changes in oestrus cycle, mating rate, conception rate, gestation time or birth due to the test substance could not be determined. The deaths of all offspring of a dam lead to low values of non-dead offspring and the 4 -day survival rate. Other changes in live birth rate, general findings, examination of body surface area, body weight and autopsy, which could be attributed to the test substance, could not be determined.

This gives the following NOEL and NOEAL for 2,3,5-trimethylhydroquinone under the given experimental conditions. The NOEL and NOEAL for repeated-dose toxicity in males is 10 mg / kg / day because of death in the 300 mg / kg group and elevated levels of hemosiderin dye in the spleen in the 60 mg /kg group were found. In females, the value is 60 mg / kg / day since deaths and increased levels of hemosiderin dye in the spleen were noted in the 300 mg / kg group. Concerning. Reproductive toxicity of NOEL and NOEAL in males is 300 mg / kg / day, as no change could be detected. In dams and the F1 generation, the value is 60 mg / kg / day as low rates of birth rate, corpus luteum, survivability of

offspring and one death of all offspring of a dam were found.

Reference 2

Endpoint:

two-generation reproductive toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1993

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 416 (Two-Generation Reproduction Toxicity Study)

Deviations:

not specified

GLP compliance:

not specified

Specific details on test material used for the study:

>99% w/w

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

test solution prepared before each dosing
analytical verification of the test material periodically

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

test solution prepared before each dosing

Duration of treatment / exposure:

10 weeks prior cohabitation

Frequency of treatment:

once daily 7 days a week

Dose / conc.:

15 mg/kg bw/day (nominal)

Dose / conc.:

50 mg/kg bw/day (nominal)

Dose / conc.:

150 mg/kg bw/day (nominal)

No. of animals per sex per dose:

30

Control animals:

yes

Postmortem examinations (parental animals):

males: tetstes with epidymides, seminal vesicles prostate glandpituitary gland and grosse lesions
females vagina, uterus, ovaries, pituary gland and gross lesions

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

mild transient tremors at 150 mg/kg bw

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Description (incidence and severity):

at several intervals

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Description (incidence and severity):

mild tremors in doeses 50 and 150 mg/kg bw.

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

no microscopic lesions attributable to HQ were found in tissues from FO or Fl parental animals subjected to histopathologie examinanon.
(da ta not shown).

Histopathological findings: neoplastic:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

not specified

Reproductive performance:

no effects observed

Description (incidence and severity):

Reproductive performance was not adversely affected by administration of HQ over two generations.

Key result

Dose descriptor:

NOEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Key result

Critical effects observed:

not specified

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

mild tremors

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No statistically significant differences in body weights were observed for FO or Fl parental females throughout the study

Organ weight findings including organ / body weight ratios:

not examined

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Key result

Dose descriptor:

NOEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Critical effects observed:

no

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

mild termors

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No statistically significant differences in body weights were observed for FO or Fl parental females throughout the study

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not examined

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 examined

Gross pathological findings:

no effects observed

Description (incidence and severity):

Upon gross postmortem examination, no treatment-related lesions were observed in either FO and FI parental animals or F 1 and F2 pups,

Description (incidence and severity):

no microscopic lesions attributable to HQ were found in tissues from FO or Fl parental animals subjected to histopathologie examinanon (da ta not shown).

Behaviour (functional findings):

no effects observed

Key result

Dose descriptor:

NOEL

Generation:

F1

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

sexual maturation

Remarks on result:

not determinable due to adverse toxic effects at highest dose / concentration tested

Critical effects observed:

no

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Behaviour (functional findings):

no effects observed

Developmental immunotoxicity:

not examined

Key result

Dose descriptor:

NOEL

Generation:

F2

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Critical effects observed:

no

Key result

Reproductive effects observed:

no

Lowest effective dose / conc.:

150 mg/kg bw/day (nominal)

Treatment related:

yes

Conclusions:

The results of the present study indicate that HQ is not a selective reproductive toxicant. The estimated NOEL for reproductive toxicity is 150 mg/kg/day,

Executive summary:

Gavage administration of HQ at 150 mg/kg/day produced evidence of slight toxicity in parental animals. Several F0 and F1 high-dose parental animals occasionally exhibited mild, transient tremors shortly after dosing. In a subchronic neurobehavioral study, Topping et al. (1991) reported observing tremors in Sprague-Dawley rats at 64 and 200 mg/kg/day within a few hours after dosing. Administration of HQ through two consecutive generations did not produce any adverse effects on reproductive performance or litter or pup parameters. These results are consistent with those previously reported by Ames et al. (1956) who saw no adverse effects on fertility, gestation, length, mean litter size, or viability following administration of HQ to female rats at dietary levels up to 3000 ppm. Further, in a developmental toxicity study in rats, pregnancy rates. mean numbers of corpora lutea, implantation sites. viable fetuses. and early and late resorptions, and fetal development were not affected following gavage administration of HQ on gestation days 6 through 15 at doses as high

as 300 mg/kg/day (Krasavage et al . 1992). However, other researchers have reported a prolonged diestrus phase in female rats receiving 200 mg HQ/kg/day by gavage (Racz et al. 1958), an increase in fetal resorptions (Telford et al., 1962), and reduced reproductive performance in male rats receiving 300 mg/kg/day st: (Skalka, 1965). The prolonged diestrus phase reported by Racz el al. ( 1958) may have been a secondary elfect due to severe systemic toxicity observed at 200 mg/kg. Also. the use of higher doses and differences in purities of hydroquinone tested, duration and routes of exposure, and strains of rats could account for these conflicting results. The results of the present study indicate that HQ is not a selective reproductive toxicant. The NOELs for general and reproductive toxicity are 15 and 150 mg/kg/day, respectively.

Reference 3

Endpoint:

two-generation reproductive toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 416 (Two-Generation Reproduction Toxicity Study)

Version / remarks:

In recognition of the known adverse effects of resorcinol on the TG, the study design went beyond the regulatory testing guidelines by including expanded thyroid functional assessments.

GLP compliance:

not specified

Specific details on test material used for the study:

> 99.8 w/w

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male/female

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

drinking water ad libitum containing 120, 360, 1000, and 3000 mg/L

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

For the F0 generation five groups of 30 males and 30 females were mated to yield at least 20 pregnant females per group at or near term. Upon study initiation all rats had drinking water available at all times that contained resorcinol at concentrations of 0, 120, 360, 1000, and 3000 mg/L. These resorcinol exposure concentrations for the full two-generation reproduction study were arrived at by preceding palatability assessments of short duration (2 weeks). The drinking water concentrations were raised up to 10000 mg/L, a level that was not accepted by the rats. By contrast the concentration of 3000 mg resorcinol/L was tolerable and was designated as the maximum palatable concentration, which was selected as the top concentration.

Frequency of treatment:

drinking water ad libitum

Dose / conc.:

120 mg/L drinking water

Dose / conc.:

360 mg/L drinking water

Dose / conc.:

1 000 mg/L drinking water

Dose / conc.:

3 000 mg/L drinking water

Remarks:

The average daily intake of resorcinol in the 3000 mg/L animals across both generations ranged from 233 mg/kg for males to 304 (premating and gestation) and 660 (lactation) mg/kg for females (Table 1). Profoundly increased water consumption with concomitantly much higher intake of a water-delivered test chemical during lactation is commonly observed in nursing animals (Christian et al. 2002a, 2002b).

No. of animals per sex per dose:

For the F0 generation five groups of 30 males and 30 females were mated to yield at least 20 pregnant
females per group at or near term.

Control animals:

yes

Oestrous cyclicity (parental animals):

Estrous cyclicity was monitored by daily vaginal lavages and light microscopy. The slides from each F0 and F1 female were evaluated daily, beginning 3 weeks prior to pairing and continuing until mating was observed.

Sperm parameters (parental animals):

Samples of sperm from the right epididymis were collected from each adult F0 and F1 male and evaluated for the percentage of progressively motile sperm. Motile sperm were evaluated using the Hamilton-Thorne HTM-IVOS (IntegratedVisual Optical System)Version 12.1 computer-assisted sperm analysis (CASA) system. Sperm morphology was evaluated by light microscopy with modifications of the wet-mount evaluation technique (Linder et al. 1992).The left testis and epididymis of all F0 and F1 males in all groups was evaluated for homogenization-resistant spermatid head counts and daily sperm production rate (testis only; Blazak, Ernst, and Stewart 1985) using the HTM-IVOS system.

Litter observations:

Number of newborns, live litter sizes, newborn body weights and weight changes were observed.

Postmortem examinations (parental animals):

Surviving F0 and F1 adults were necropsied once their offspring had been weaned. The stage of estrus on the day of study terminationwas determined for all F0 and F1 females in the control and 3000 mg/L groups. Selected F0 and F1 parental tissues and organs were fixed by immersion in neutral-buffered 10% formalin for possible histopathological examination.
Microscopic evaluations were performed on the following tissues of all F0 and F1 parental animals from the control and high-exposure groups and those that had died or were euthanized in extremis: adrenal glands, cervix, right epididymis (caput, corpus, and cauda), coagulating gland, ovaries, oviducts, pituitary gland, prostate gland, seminal vesicles, stomach, right testis, thyroid gland, uterus, vagina, and gross internal lesions (all groups).

Postmortem examinations (offspring):

All offspring were examined for external malformations on PND 0. Stillborn and intact offspring, dying between PNDs 0 and 4, were necropsied using a fresh tissue dissection technique (Stuckhardt and Poppe 1984). A detailed gross necropsy was performed on any offspring dying after PND 4 and prior to weaning.

Statistics:

All statistical analyses were conducted using two-tailed tests (except as noted below) for a minimum significance level of 5%, comparing each resorcinol-exposed group to the control group. Data obtained from nongravid animals were excluded from statistical analyses.

Reproductive indices:

Conception- and copulation indices were evaluated.

Clinical signs:

no effects observed

Mortality:

no mortality observed

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

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Key result

Dose descriptor:

NOEL

Effect level:

1 000 mg/L drinking water

Based on:

test mat. (dissolved fraction)

Sex:

male/female

Basis for effect level:

clinical biochemistry

Clinical signs:

no effects observed

Mortality:

no mortality observed

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

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Key result

Dose descriptor:

NOEL

Effect level:

1 000 mg/L drinking water

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Critical effects observed:

no

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

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

effects observed, treatment-related

Developmental immunotoxicity:

not examined

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

1 000 mg/L drinking water

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Key result

Critical effects observed:

no

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Key result

Dose descriptor:

NOEL

Generation:

F2

Effect level:

1 000 mg/L drinking water

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

Key result

Reproductive effects observed:

no

Conclusions:

The 3000 mg/L resorcinol exposure level was the no-observed-adverse-effect level (NOAEL) for parental systemic and offspring toxicity, while 1000 mg/L was the no-observed-effect level (NOEL). The average daily intake of resorcinol in the 3000 mg/L animals across both generations ranged from 233 mg/kg for males to 304 (premating and gestation) and 660 (lactation) mg/kg for females. The average daily intake of resorcinol in the 1000 mg/L animals across both generations ranged from 86 mg/kg for males to 126 (premating and gestation) and 225 (lactation) mg/kg for females.
A NOEL on base of mean intake of 160 mg/kg bw was derived.

Executive summary:

The potential adverse effects of resorcinol, applied via drinking water at 0, 120, 360, 1000, and 3000 mg/L (palatability limit), were assessed in a regulatory guideline compliant two-generation reproduction study in Crl:CD(SD) rats. Expanded end points of thyroid gland (TG) function were added because of clinical case reports indicating human TG toxicity. Average daily resorcinol intake (mg/kg) at the 3000 mg/L concentration was 233 in F0 and F1 males, whereas in females it was 304 (premating/gestation) and 660 (lactation). No resorcinol ingestion-related clinical signs of toxicity were observed. Furthermore, neither gross morphologic anomalies nor effects on reproductive function or thyroid hormone levels were detectable. Body weight reductions occurred in 3000 mg/L F0 and F1 animals and were more pronounced in males.

However, there was no evidence of either cumulative toxicity in the second generation or of enhanced sensitivity to resorcinol in pregnant/lactating females. Water intake was lower in 3000 mg/L rats of both generations and intermittently, to a lesser extent, at 1000 mg/L; however, concurrent feed intake and utilization were unaffected. Decreased TG follicular colloid content (conventional histopathology; confirmed by quantitative stereomicroscopy) in the 3000 mg/L F0 males was attributed to resorcinol but not considered adverse. The 3000 mg/L intake level appeared to have caused an adaptive thyroid response to a new homeostatic level with no adverse physiological consequences in either males (the more susceptible gender) or females. There were no differences in TG histology in F0 rats of either sex at 1000 mg/L. Thus, resorcinol intake at maximum palatability via a route and mode relevant to potential human exposures via contaminated drinking water at presently unknown environmental concentrations caused no detectable adverse effects on any reproduction or TG end points. The 3000 mg/L resorcinol exposure level was the no-observed-adverse-effect level

(NOAEL) for parental systemic and offspring toxicity, while 1000 mg/L was the no-observed-effect level (NOEL).

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

75 mg/kg bw/day

Study duration:

subchronic

Species:

rat

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

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available