2H-Benzimidazole-2-thione, 1,3-dihydro-ar-methyl-, sodium salt (1:1)

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

A Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test (OECD TG 422) in rats by the oral route (dietary) with the read-across substance ZMB2 (CAS 61617-00-3) resulted in a LOAEL value for fertility of 60 mg/kg/day.

Based on preliminary data from the ongoing extended one-generation reproductive toxicity study (OECD TG 443) with the read-across substance ZMB2, fertility effects have been observed. As this study is ongoing not all data are available at this point in time. Study data has not been populated in IUCLID as the study is ongoing, and it is not possible to partially populate a study summary and still pass the technical completeness check.

The dose levels administered to F0 and F1 generation rats were 5, 15, and 40 mg/kg/day. Duration and timing of treatment as well as all aspects of the study followed the OECD TG 443.

Among the F0 generation rats treated with a dose level of 40 mg/kg/day, three cases of dystocia were observed and considered treatment-related. For F1 litters, live litter size on Day 1 of age was lower than control at 40 mg/kg/day. In addition, post-implantation survival index was lower than control in all groups of treated females, although in the absence of a dose response relationship. Despite these changes, the mean number of implantations were essentially similar in all groups. It is not known whether these findings in the F1 litters were related to changes seen in the F0 generation rats, which include changes in kidney weights (40 mg/kg/day) and thymus weights (15 and 40 mg/kg/day). No other findings were found to be significant so far.

The main, leading toxicological effect at this point in time is dystocia. This effect is observed at doses ≥ 40 mg/kg/day; not at 15 or 5 mg/kg/day.

Since the F0 animals breeding phase is completed the dystocia data will not change for the first breeding and, consequently, the NOAEL for dystocia is 15 mg/kg/day at this point in time.

Once all data on this OECD 443 study will be available, a definitive NOAEL will be derived.

Link to relevant study records

Reference

Endpoint:

fertility, other

Remarks:

based on test type (migrated information)

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

other information

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: secondary literature - cited from OECD SIDS and US EPA

Qualifier:

according to guideline

Guideline:

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

Principles of method if other than guideline:

In a combined, repeated-dose reproductive/developmental toxicity study, Sprague-Dawley rats (10/sex/dose) were administered CASRN 61617-00-3 orally in the diet at 1000, 2750 or 7500 ppm (~ 50, 138 or 375 mg/kg-bw/day). Treatment began two weeks prior to mating and continued throughout gestation, up to postnatal day 5 (~ 47 days). Doses were reduced to 900, 2500 or 6750 ppm on day 29 (~ 45, 125 or 338 mg/kg-bw/day) and on day 33, the high-dose group was further reduced to 5500 ppm (~ 275 mg/kg-bw/day) due to observed toxicity (type not specified in robust summary).

GLP compliance:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Route of administration:

oral: feed

Vehicle:

other: diet

Details on mating procedure:

Following 2 weeks of dosing, male and female rats were paired within their dose groups to produce litters

Duration of treatment / exposure:

Treatment began 2 weeks prior to mating and continued throughout gestation, up to postnatal day 5 (ca. 47 days)

Frequency of treatment:

daily

Details on study schedule:

At day 5 post partum, all surviving females, males and offpring were killed and examined macroscopically

Remarks:

Doses / Concentrations:
1000, 2750 or 7500 ppm (ca. 50, 138 or 375 mg/kg bw/day) day 1-28
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
900, 2500 or 6750 ppm (ca. 45, 125 or 338 mg/kg bw/d) day 29-32
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
high dose group was further reduced to 5500 ppm (ca. 275 mg/kg bw/d) day 33-45
Basis:
nominal in diet

No. of animals per sex per dose:

10/sex/dose

Control animals:

yes, concurrent vehicle

Dose descriptor:

LOAEL

Effect level:

45 - 50 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: based on increased gestation lenght

Dose descriptor:

NOAEL

Effect level:

275 - 338 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: based on no effects observed at the highest dose tested

Reproductive effects observed:

not specified

The combined repeated-dose reproductive/developmental toxicity study showed both systemic and reproductive toxicity in orally exposed rats. Significant decrements in body weight gain and organ weights were observed at all levels of treatment, including the lowest dose tested (45-50 mg/kg/day). Female reproductive toxicity, as evidenced by increased gestation length, occurred at all doses. The NOAEL for male reproductive toxicity was approximately 275-338 mg/kg/day, based on no effects at the highest dose tested. Developmental toxicity could not be evaluated due to a high incidence of mortality in the dams.

Executive summary:

The administration of Vanox ZMTI to male and female rats at dose levels of up to 7500 ppm (~ 375 mg/kg bw/d) (adjusted to 6750 ppm (~ 338 mg/kg bw/d and then to 5500ppm (~ 275 mg/kg bw/d)) for a period of up to forty seven days; which included a mating period, gestation and early lactation phase, resulted in treatment-related upon mating performance, fertility and the parturition process. The "No Observed Adverse Effect Level" (NOAEL) for reproductive effects upon adults was not established.

The LOAEL for systemic toxicity = 45 -50 mg/kg bw/d.

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

45 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

secondary literature

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

In the combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test, signs of systemic toxicity, body weight, food consumption, blood chemistry and hematological parameters, organ weights and histopathological examinations were recorded. Additional: corpora lutea of all ovaries from pregnant females and uterine implantation were counted at necropsy. Pre-coital interval, mating index, pregnancy index, gestation lenght, parturition index, laive birth index, viability index and sex ration were calculated.

During the course of the study there were a total of nine females that were killed in extremis. One female from the high dose and eight from the intermediate dose level. All mortalities were associated with pregnant females particularly during late gestation at and around the time of parturition.

 

At the high dose level, clinical signs of toxicity were observed during treatment for both sexes; these signs were considered not to be indicative of behavioural or neurotoxic effect.

 

There was also evidence of significant reductions in both bodyweight gain and food consumption prior to mating and persisted for males post mating. The findings from the blood chemistry evaluations showed alterations in plasma concentrations of phosphorus and chloride for both sexes plus increased plasma creatinines for males. These findings were not associated with any significant renal pathology. The observed blood chemistry changes together with an increase plasma cholesterol, reduced adrenal weights for both sexes plus histopathological changes to the liver and thyroid glands are symptomatic of altered metabolic state. This may well be a direct consequence of test material metabolism or as a consequence of the reductions in weight gain and food consumption. The splenic changes for males and females seen at histopathology and with the organ weight decrements does not appear to be associated with any significant haematological changes. The slight variations in clotting time and platlet count for males or females may be a consequence of potential alterations in hepatic or general metabolism that may have a secondary effect upon clotting factors.

 

At histopathology, the hypertrophy observed for the liver of both sexes may be indicative of enhanced metabolism from xenobiotic administration. The thyroid gland hypertophy may also be a consequence of a negative feedback via enhanced metabolism of circulating thyroid hormones. The histopathological changes tend to support the proposal of an altered metabolism being the principal sytemic effect seen following administration of test material. The splenic changes seen may be associated with the altered physiologic status of the animals from reductions in bodyweight and food consumption. Other treatment related histopathological changes to the salivary glands and pituitary are of note because of the treatment and dosage relationship but are not indicative of a specific toxic effect. Organ weight analysis showed decrements for a number of organs for males at termination, which were primarily a consequence of reduced bodyweight. Elevated relative liver weight was connected to they hypertrophy observed at histopathology, which may be a result of alterations in metabolic status.

 

The results of the mating performance of the males and females show significant treatment-related effects. There is evidence to suggest that normal reproductive behaviour has been affected at this dose level. The mating pairs with no positive evidence of mating showed the females to generally not exhibit normal oestrous cycling. Of the mating pairs where positive evidence of mating was observed, pregnancy was established in 50% of these. Histopathology of the reproductive organs showed no specific effects. The live litter size at birth was low for the small number of females that gave birth. Offspring bodyweight appeared unaffected by treatment but the number of offspring evaluated did not allow a meaningful assessment to be conducted. The overall conclusion was that reproductive performance was affected from the conception phase to parturition. These effects were seen at a dose level that was toxic to the adult and therefore reproductive failure was a consequence of the toxicity seen.

 

At the intermediate dose level similar clinical signs of toxicity were observed but at a lower incidence. Effects upon bodyweight gain and food consumptions were also observed. A similar profile of effects were seen for blood chemistry, organ weight and histopathological changes indicating a treatment and dosage relationship. There were no effects upon mating performance of fertility when compared to the highest dose level. The most important finding was sufficient to inhibit delivery of the offspring. An evaluation of offspring bodyweight at birth shows that the foetus/neonate has not been directly affected by the test material.

 

At the low dose level there were indications of test material effects upon the adult. There were slight reductions in bodyweight change at various time points during the study for either or both sexes. In addition, there were slight reductions in food consumption at various time points including females during gestation. Similar changes to that seen at higher dose levels were observed for the blood chemistry and histopathology evaluations. There appears to be a treatment and dosage relationship.

 

Mating performance and fertility were not affected by treatment. There was a slight reduction in group mean live litter size at birth together with an increase in post implantation offspring loss. These results were not statistically significant because of a large intragroup variability. These results are of significance because of reproductive effects seen at higher dose levels and cannot therefore be ignored (as discussed by the authors of the Dietary Combined Repeat Dose Toxicity Study with Reproduction/Developmental Screening Test in the Rat).

The LOAEL (female rats) was 45 -50 mg/kg bw/d based on increased gestation lenght. The NOAEL (male rats) was 275 -338 mg/kg bw/d based on no effects observed at the highest dose tested.

In the subacute 28 day study reproductive organs of the rats were examined histopathologically. No adverse effects were reported from these organs. Based on these results there are no indications for specific adverse effects on the reproductive organs up to 100 mg/kg bw/day (highest applied dose).

Short description of key information: A combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test (read-across from 2-mercaptomethylbenzimidazole, zinc salt CAS 61617-00-3) and an oral 28 d repeated dose study where the reproductive organs were histopathologically examined are available.

An extended one generation study with 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt (ZMB2, CAS 61617-00-3) is ongoing.

Effects on developmental toxicity

Description of key information

no data

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

Additional information

no data

Toxicity to reproduction: other studies

Additional information

no data

Justification for classification or non-classification

Based on the results of the combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test a preliminary classification for fertility as Repr. Cat.2, (H361: Suspected of damaging fertility or the unborn child) is adequate, as reproductive performance was affected from the conception phase to parturition.

However, based on preliminary data from the ongoing extended one-generation reproductive toxicity study (OECD 443) with the read-across substance ZMB2, NaMB2 (CAS 75045-07-7) is being classified as a category 1B reproductive toxicant. A robust summary has not been created as the study is still ongoing and the IUCLID system will not accept the creation of a summary from a partially complete study.

Classification is justified as in the main OECD 443 study dystocia was observed amongst dams at the top dose.

Since dystocia is a discrete event, no additional information created in the study will refute or confirm the finding, and thus immediate classification is deemed necessary.