LBX98

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Justification for type of information:

The reproductive toxicity of the individual (o-, m- and p-) cresol isomers has been investigated in three separate two-generation toxicity studies. No effects on fertility were seen in any study at the high dose level of 450 mg/kg bw/d. General toxicity (increased mortality and in clinical signs including hypoactivity, ataxia, twitches, tremors, prostration, gasping, rapid respiration and perioral wetness) were observed at dose levels of 175 and 450 mg/kg bw/d, resulting parental NOAELs of 30 mg/kg bw/d. Reduced pup weight and viability were seen at the highest (and parentally toxic) dose level of 450 mg/kg bw/d, leading to NOAEL values of 175 mg/kg bw/d. OECD 422 screening studies available for xylenol (mixed isomers) and ethylphenol (mixed isomers) both report and absence of effects on fertility and reproductive NOAEL values of 245 mg/kg bw/d. The Category substances therefore consistently demonstrate a lack of reproductive toxicity. Read-across is therefore proposed to the study with xylenol as the closest structural analogue among the Category members.
Developmental toxicity studies in the rat are available for the individual (o-, m- and p-) cresol isomers. Each study identified significant maternal toxicity (mortality, clinical signs, bodyweight deficits) at the high dose level of 450 mg/kg bw/d, resulting in maternal NOAELs of 175 mg/kg bw/d for each isomer. Slight fetotoxicity was observed at 450 mg/kg bw/d for o-cresol (one visceral variation: dilated lateral ventricles of the brain) and for p-cresol (reduced foetal weight, reduced skeletal ossification). There were no foetal effects with m-cresol at any dose level.

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: TSCA Health Effects Test guidelines for Specific Organ/Tissue Toxicity - Developmental Toxicity (EPA, 1984,1987)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Reaction mass of 2,4-xylenol and 2,5-xylenol

EC Number:

905-287-4

Cas Number:

1638758-52-7

Molecular formula:

(CH3)2C6H3OH

IUPAC Name:

Reaction mass of 2,4-xylenol and 2,5-xylenol

Test material form:

solid: bulk

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS- Source: Charles River Breeding labarotory, Kingston, NY- Age at study initiation: 56 days at arrival- Weight at study initiation: 228-231g- Housing: after mating: singly- Diet : ad libitum - Water : ad libitum- Acclimation period: 2 weeksENVIRONMENTAL CONDITIONS- Temperature (°F): 72- Humidity (%): 40 - 60- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:Dosing formulations were prepared by weighing the amount of test chemical into a volumetric flask and diluting to volume with certified corn oil. The resulting solutions were mixed by repeated inversions and stored at room temperature.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

A standard stock solution (1 mg/ml) was prepared as needed by weighing 50 mg m-cresol into a 50 ml volumetric flask and diluting to volume with propanol. Standards ranging from 10 to 100 ng/ml were prepared by diluting the stock solution with propanol. 10 µl of each standard was injected onto the HPLC. the actual conentration of each dosing solution was calculated from the equitation for the standard curve developed by linear regression.

Details on mating procedure:

- Impregnation procedure: cohoused- If cohoused: - M/F ratio per cage: 1:1 - Verification of same strain and source of both sexes: yes- Proof of pregnancy: vaginal plug referred to as day 0 of pregnancy:

Duration of treatment / exposure:

day 6 through day 15 of gestation

Frequency of treatment:

daily

Duration of test:

gd 21 (scheduled sacrifice)

No. of animals per sex per dose:

25 females/ group, 50 control females

Control animals:

yes, concurrent vehicle

Details on study design:

no further data

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes - Time schedule: daily- Cage side observations : mortalityDETAILED CLINICAL OBSERVATIONS: Yes - Time schedule: twice dailyBODY WEIGHT: Yes- Time schedule for examinations: : gd 0, 6, 11, 15, 21FOOD CONSUMPTION Yes - Food consumption for each animal determined throughout gestation gd 0-21WATER CONSUMPTION NoPOST-MORTEM EXAMINATIONS: Yes- Sacrifice on gestation day 21 - Organs examined: body weight, liver, gravid uterine weight, number of corpora lutea, number and status of implantaion sitesOTHER:

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes Examinations included:- Gravid uterus weight: Yes - Number of corpora lutea: Yes - Number of implantations: Yes - Number of early resorptions: Yes - Number of late resorptions: Yes

Fetal examinations:

- External examinations: Yes: all per litter- Soft tissue examinations: Yes: half per litter- Skeletal examinations: Yes: half per litter- Head examinations: Yes: half per litter

Statistics:

Levene's test, ANOVA, t-test with Bonferroni prohabilities, Kruskal-Wallis test, Mann-Whitney U test, Fishers exact test

Indices:

no data

Historical control data:

no data

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yesDetails on maternal toxic effects:no mortality,no treatment-related abortions or early delivery, no treatment related lesions in dams at scheduled sacrifice450 mg/kg bw/day (significant canges only)significant reduction in mean maternal body weights:gd 11: 261 g versus 276 g in controlsgd 15: 281 g versus 300 g in controlsreduction in mean weight gain during dosingreduced mean gestational weight gaingd 0-21: 145 g versus 163 g in controls clinical signs of toxicity : predominantly hypoactivity, ataxia, tremors, twitches, prone positioning, audible rtespiration, perioral wetnessreduction inmean food consumptionpretratment period: day 6-9: 15 g versus 21 g of controlstreatment period gd 6-15 : 19 g versus 22 g of controlsrelative (not absolute) liver weight was increased4.9 % versus 4.52 % in controls

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

ca. 175 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effectsDetails on embryotoxic / teratogenic effects:no effects

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

450 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Fetal abnormalities

Key result

Abnormalities:

no effects observed

Overall developmental toxicity

Key result

Developmental effects observed:

no

Any other information on results incl. tables

RS-Freetext:

maternal toxicity: no deaths, no abortions or early deliveries

 

450 mg/kg:

significant reduced food consumption, reduced maternal body weights and weight gain during dosing period; reduced gestational weight gain (day 0-21);

 

clinical signs of toxicity: hypoactivity, ataxia, tremors, audible respiration, perioral wetness; increased relative but not absolute liver weights no embryotoxicity or teratogenicity was observed at any dosage level

Applicant's summary and conclusion

Executive summary:

Developmental toxicity study according to TSCA Health Effects Test guidelines for Specific Organ/Tissue Toxicity - Developmental Toxicity (EPA, 1984,1987):

Administration of m-cresol by gavage to time-pregnant-Sprague Dawley rats during organogenesis at 0.0, 30, 175, 450 mg/kg bw/d resulted in maternal toxicity at 450 mg/kg bw/day including significant reduction in periodic maternal body weights and weight gain during the dosing period in addition with clinical signs of toxicity (NOAEL (maternal toxicity) 175 mg/kg bw/d). m-Cresol did not induce fetotoxicity or malformations at any dose level tested. (NOAEL (developmental toxicity) >450 mg/kg bw).

The above results are suitable to be used for read across for Reaction mass of 2,4-xylenol and 2,5-xylenol, due to the category being based on structural similarity and comparable physicochemical properties, leading to similar (eco)toxicological properties.