Teflubenzuron

Endpoint summary

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Effects on fertility

Description of key information

2-Generation reproduction toxicity study: NOAEL 500 ppm (highest concentration tested, no adverse effects on reproductive toxicity observed)

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

36.9 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

According to EPA Guideline 83-4 (1982) and equivalent to OECD Guideline 416, conducted under GLP (incl. QA statement).

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

The potential of the test substance to cause effects on fertility was investigated in a two-generation reproductive toxicity study according to EPA guideline 83-4 and equivalent to OECD guideline 416, conducted according to GLP.

Sprague-Dawley rats, 25 per sex and dose, were administered daily doses of 0, 20, 100 or 500 ppm test substance via the diet. Following 70 days of pretreatment, the parental (P generation) animals were mated 1:1 for a maximum of 14 days. Successful mating was determined via the presence of sperm in the vaginal smear. Females were then monitored throughout gestation and littering. Litters were standardized on day 4 post partum to 5 males and 5 females if possible. At the age of 80-90 days, F1 generation animals were mated in the same fashion as the parental animals. Again, females were monitored throughout gestation and F2 pups were observed until weaning.

P generation:

No abnormalities of clinical condition were observed. There were no treatment-related mortalities of the parental animals. Body weight gain for males during the premating period was similar in all groups. Body weight gain of females during premating, gestation, and lactation period was comparable in all groups. Mean food consumption in the treated groups was similar to the controls for both sexes. Isolated findings in the urinary tract of both sexes were considered not related to treatment. Similarly, in both control and high dose group one female each presented with complete intrauterine litter loss, which was considered not substance-related. All histopathological lesions observed were considered incidental and not related to treatment. There was no effect of treatment on mating performance or fertility. All pregnant animals littered on gestational days 21 or 22. The mean duration of gestation was normal in all groups.

P1 generation:

No treatment-related changes in appearance, behaviour, and general condition were observed. No mortality was reported. Some variations were observed in the body weights / body weight gains between control and treated groups, however these effects were not dose-related and therefore considered non-treatment-related. Mean food consumption in the treated groups of males and females was comparable with the control group. The necropsy revealed a few isolated findings in the urinary tracts of both males and females which were considered not related to treatment. All histopathological findings were considered incidental and not related to treatment. There was no effect of treatment on mating performance or fertility. The mean duration of gestation was comparable in all groups.

F1 generation:

Between day 1 and day 4 post partum, isolated F1 pup losses were observed in all groups. After adjustment of litter size (day 4 post partum), pup loss was similar in all groups. Mean pup weight was similar in all groups. No relevant differences in food consumption were observed. Concerning all physical development parameters examined (pinna unfolding, hair growth, incisor eruption, eye opening), the onset of the observations was comparable in all groups. The employed functional tests (pupillary reflex, startle response, water maze) revealed no treatment-related effects.

F2 generation:

Between day 1 and day 4 post partum, isolated F2 pup losses were observed in all groups. After adjustment of litter size (day 4 post partum), pup loss was low and showed no significant intergroup variation. Mean pup weight was similar in all groups. Concerning all physical development parameters examined (pinna unfolding, hair growth, incisor eruption, eye opening), the onset of the observations was comparable in all groups.

 

Based on the data obtained in the present study, no effects on mating performance or fertility as well as post-natal development were observed at doses of 500 ppm test substance administered via the diet. Therefore, the NOAEL for fertility is at least 500 ppm (corresponding to ≥ 36.9 mg/kg bw/d).

Effects on developmental toxicity

Description of key information

rat: NOAEL 1000 mg/kg bw/d

rabbit: NOAEL 1000 mg/kg bw/d

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

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

The test substance was assessed for the potential to affect embryonic and fetal development in both rats and rabbits.

 

Rats:

In rats, two developmental toxicity studies were conducted.

 

In the first study, conducted similar to OECD 414 and according to GLP, the test substance was administered in doses of 0, 10, 50, or 250 mg/kg bw/d in 0.5% CMC to Wistar dams from gestation days (GD) 6-15. On GD20, a caesarian section was performed and both the maternal reproduction parameters (number of implantation sites, abortions, resorptions, pre-and post-implantation losses) as well as fetal developmental parameters (weight, number, sex, as well as external, skeletal, and visceral malformations) were assessed.

In all treated groups, dams did not show clinical signs of toxicity. Nevertheless, the doses were considered sufficiently high since at similar concentrations in 28-day toxicity studies, liver effects were observed. However, since neither the liver nor clinical chemistry parameters of the dams were investigated, this cannot be verified under the settings of this developmental toxicity study. Food consumption and body weight of the dams was not affected by treatment. At the end of the study, no gross pathological changes were observed in the dams.

In terms of maternal developmental parameters, no effects on resorptions, pre- or post-implantation losses, and no increases in dead fetuses were observed between treated and control groups. However, in the high dose group, an increased number of dams with total litter loss was observed as compared to controls (3 in high dose vs. 0 in the control group). This was not a dose-dependent effect, since total litter losses were also observed in the low dose, however not in the mid dose. The number of pups lost was not remarkably increased as compared to the historical controls (1.5% pups aborted as compared to implantations in historical control group vs. 2.1% pups aborted as compared to implantation sites in the high dose group). One of the dams with complete litter loss presented with vaginal bleeding on day 12, no clinical signs were recorded for the other dams. Remarkably, all dams with total litter loss had very few pups to begin with. In combination with high discrepancies between the number of corpora lutea and the number of implantation sites in all dams, this raises the question whether the mating phase was sufficiently successful or whether the animals were in some way predisposed in a non substance-related manner. Since implantation is finished upon substance administration, the substance should have no influence on the number of implantation sites in the test protocol described. Altogether, the relevance of the increased abortion finding remains unclear, therefore these data will be assessed together with the findings obtained in the second developmental toxicity study.

Fetuses did not show any effects of treatment regarding mean fetal body weights, litter size and litter weights. The number of live offspring was reduced in the high dose group due to the complete litter losses observed. Additionally, the sex ratio was slightly changed in all treated groups compared to the concurrent control, however it was similar to the historical control, therefore this finding was considered incidental and not treatment-related.

 

In a second study conducted similar to OECD guideline 414 and GLP, Wistar dams (25 per group) were administered the test substance at doses of 0, 100, 300, or 1000 mg/kg bw/d in 0.5% CMC from GD 7-17. On GD20, a caesarian section was performed and both the maternal reproduction parameters as well as fetal development parameters were assessed.

None of the dams did show clinical signs of toxicity. Body weights and food consumption of treated animals were similar to the control group. No abnormalities of any kind were observe din the gross pathological examination of the dams. No significant variations were observed with respect to the number of corpora lutea, number of implantations, number of dead and resorbed fetuses, number of live fetuses, and placental weight. The fetuses did not show significant differences with regards to the sex ratio and body weights of live fetuses. No external abnormalities were observed. The instances of visceral abnormalities were comparable between all groups, the most frequent abnormality observed was thymic remnants in the neck. None of the visceral abnormalities recorded could be associated with test substance administration. Skeletal examination of the fetuses slightly higher incidences of abnormalities in the high dose group as compared to the control. The most frequently observed abnormality in the high dose group was the occurrence of a 14th rib. However, out of the 21 instances of 14th rib, 11 were concentrated in two dams and since the rate of natural occurrence in Wistar rats is 6.01 ~ 15.5% and the present rate of occurrence, 11.4%, lies within that range, this was considered to be accidental variation. Therefore, it was considered that the rate of occurrence of fetuses having skeletal malformations was also accidental.

 

Since no increased rate of abortions was observed in the second study although the animals were administered 4 times higher doses than in the first study, while the same animal strain, vehicle and route of administration was used, it can be concluded that the increased abortion rate observed in the high dose animals in the first study was incidental and  related to technical difficulties in the study conduct (e.g. low numbers of pups to begin with and/or problems during the mating period) rather than being a substance-specific effect.

Overall, the NOAEL for developmental toxicity in rats was set at 1000 mg/kg bw/d based on a lack of toxic effects in the second study.

 

 

Rabbits:

The potential of the test substance to cause developmental toxicity in rabbits was tested in two independent sets of experiments.

 

In a study conducted according to US EPA Guideline 83-3 and GLP, New Zealand White rabbits were mated naturally, resulting in 38 pregnant dams. The animals were treated either with 1000 mg/kg bw/d of the test substance suspended in 0.5% CMC (22 dams) or the vehicle alone (16 dams) from gestation days 6 to 18 by daily gavage. The pregnant animals were terminated and caesarian section was performed on day 28 post coitum.

The dams did not show any clinical signs of toxicity; body weight development, food consumption and water consumption were comparable to the control group. Occasional minor necropsy findings of the liver (i.e. grossly granulated cut surface of the liver) were detected more frequently in treated dams as compared to controls. Given that the liver is a target organ for the substance, it is highly likely this is a substance-related effect demonstrating slight maternal toxicity at 1000 mg/kg bw/d, however the adversity of this effect could not be determined.

There was no effect of the treatment on the number, weight, or sex of the fetuses, or on pre- and post-implantation loss. There was no increased incidence of malformations in fetuses of treated dams as compared to those of control dams.

Therefore, both the maternal and the fetal NOAEL were set at 1000 mg/kg bw/d based on the results of this study.

 

In a second set of experiments, three independent studies similar to OECD Guideline 414 were conducted with increasing doses of test substance. The study design of all three studies was quite comparable: Female Himalayan rabbits were mated and subsequently treated with test substance suspended in CMC or the vehicle alone from gestation days 6 to 18 by daily gavage. The animals were terminated and a caesarian section was performed on day 29 post conception. The fetuses were subsequently incubated for 24 hours at 28°C and monitored for survival, which was used as an indicator for fitness. Subsequently, the progeny was terminated and the developmental parameters were analyzed.

 

In the first study, 15 female Himalayan rabbits per dose were mated and subsequently treated with 0, 10, 50, or 250 mg/kg bw/d of test substance suspended in CMC from gestation days 6 to 18 by daily gavage. The animals were terminated and a caesarian section was performed on day 29 post conception. The fetuses were subsequently incubated for 24 hours at 28°C and monitored for survival, which was used as an indicator for fitness. Subsequently, the progeny was terminated and the developmental parameters were analyzed.

No maternal clinical signs indicating toxicity were observed in treated animals. One control female presented with a complete litter loss, which was considered to be not substance-related. No changes in maternal reproduction parameters were observed; pre- and post-implantation losses and resorptions were within the range of the controls.

The number of dead fetuses at caesarian section was comparable to the controls and also the fetal weights were not impacted by treatment. During the 24 hour incubation period subsequent to caesarian section, slightly increased mortality was observed in the high dose group. Additionally, slightly increased "malformations" were observed in the high dose group, although it has to be clarified that the effects considered "malformations" in the study report are today mostly considered variations.

 

In the second study, 5-10 female Himalayan rabbits per dose were mated and subsequently treated with 0, 250, or 500 mg/kg bw/d of test substance suspended in CMC from gestation days 6 to 18 by daily gavage. Animals of the control and mid dose group (5 per dose) as well as 5 of the high dose animals were terminated on day 19 post conception. For those animals, the livers were removed, weighed and a small portion of each liver was homogenized for analysis of cytochrome C content and activity of O- and N-demethylase. Corpora lutea, number of living embryos and number of early resorptions per dam were counted. The remaining 5 animals of the high dose group were terminated and a caesarian section was performed on day 29 post conception. The fetuses were subsequently incubated for 24 hours at 28°C and monitored for survival, which was used as an indicator for fitness. Subsequently, the progeny was terminated and the developmental parameters were analyzed.

No maternal clinical signs indicating toxicity was observed in treated animals. No increases in liver weights or liver enzymes were observed, indicating that liver toxicity did not occur at doses up to 500 mg/kg bw/d in female rabbits. The number of early resorptions in the treated dams terminated at day 19 p.c. was increased, however this was not observed for the dams terminated at day 29 p.c.

Concurrently, the number of live pups in the groups terminated at the earlier time point was slightly reduced, which was not observed for the group terminated on day 29 p.c. Comparing these findings to the historical control database available in the laboratory, no significant effects were found for the treated groups. The pups from treated dams terminated on day 29 p.c. showed normal survival during the 24 hour incubation period and no increased incidences in skeletal or visceral malformations were observed.

 

In the third study, 15 female Himalayan rabbits per dose were mated and subsequently treated with 0 or 1000 mg/kg bw/d of test substance suspended in CMC from gestation days 6 to 18 by daily gavage. The animals were terminated and a caesarian section was performed on day 29 post conception. The fetuses were subsequently incubated for 24 hours at 28°C and monitored for survival, which was used as an indicator for fitness. Subsequently, the progeny was terminated and the developmental parameters were analyzed.

In contrast to other studies performed by the lab, the pregnancy rate for this study was very low (40% vs. 92%), resulting in only 5 pregnant dams in the control group and 7 pregnant dams in the treated group.

No maternal clinical signs indicating toxicity were observed in treated animals. No changes in maternal reproduction parameters were observed, pre- and post-implantation losses and resorptions were within the range of the controls.

The number of dead fetuses at caesarian section was comparable to the controls and also the fetal weights were not impacted by treatment. During the 24 hour incubation period subsequent to caesarian section, no increases in mortality were observed in the pups from treated vs those from control dams. No increased incidences in skeletal or visceral malformations were observed.

 

Taking together the information from all three studies in the second set, it can be concluded that the slight effects observed at 250 mg/kg bw/d in the first study were incidental since they could not be reproduced in either of the following studies with higher doses. Additionally, no adverse maternal toxicity and no developmental effect was observed at doses up to 1000 mg/kg bw/d.

 

Therefore, the overall NOAEL for maternal and developmental toxicity of the test substance in rabbits can be set at 1000 mg/kg bw/d.

Justification for classification or non-classification

Based on the data available and laying down the criteria specified in regulation (EC) 1272/2008 (CLP), no classification for toxicity to reproduction is warranted.