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Key value for chemical safety assessment

Effects on fertility

Description of key information

NOAEL of 200 mg/kg/day can be derived for reproductive toxicity based on the statistically signif

A negative result was obtained in a fertility study carried out in male rabbits in which animals were dosed daily with concentrations of TDCP up to 200 mg/kg/day for twelve weeks and then mated with two females during the last week of treatment. Mating, fertility, pregnancy parameters, sperm analysis and the male reproductive tract were unaffected by treatment.

Effect on fertility: via oral route
Study duration:
subchronic
Additional information

In a 2-year carcinogenicity study in rats, an evaluation was made of the male reproductive system. Only control and high dose animals were evaluated at 12 months, and no significant differences were noted at this time point. Effects were noted in the testes, epididymis and seminal vesicles in all animals at 24 months, with a trend for higher incidence in the treated groups.

An increase in interstitial cell tumours of the testes in the mid and high dose males at the 12 and 24 months was observed in this study. Therefore, it is possible that the effects observed on the testes may be secondary to an effect of the Leydig cell tumours. It should also be considered that the effects noted in the male reproductive system are only observed in animals at 24 months and, therefore, may be secondary to the natural ageing process of rats rather than a specific effect on the male reproductive system.

In addition to these points, as indicated above, no effect on the male reproductive system and no effects on fertility were observed in the fertility study in male rabbits. Therefore, based on a weight of evidence, it is considered that there is no concern for male fertility.

No evaluation of the female reproductive system was included in the 2-year carcinogenicity study with TDCP. However, the authors reported that all organs and tissues were examined microscopically in the high dose and control animals in this study. As no effects on the female reporductive organs were reported, it can rasonably be assumed that no effects were observed on the female reproductive organs in this study. Although there may be an apparent data gap for female fertility the EU risk assessment report concluded that there was no need to conduct a further study on reproductive endpoints based on the following rational “In considering this data gap, and the possible requirement for a female fertility study to address this endpoint, the available data for TDCP was reviewed. In the chronic toxicity study with TDCP, a LOAEL of 5 mg/kg was derived for repeated dose toxicity and carcinogenicity and brought forward to risk characterisation for both of these endpoints. Given the low LOAEL derived from this study, it is considered possible that any risk to female fertility will already be covered by the LOAEL for repeated dose toxicity and carcinogenicity, and the subsequent conclusions drawn for both of these endpoints.

This consideration is further supported by a study by Janer et al., (2007), where a retrospective analysis of the relationship between NOAEL’s for effects on fertility, obtained from two-generation reproductive toxicity studies, and those for repeated dose toxicity, obtained from subchronic studies, was conducted. The results showed that on average there was no, or only a small difference (less than two-fold), in the NOAEL’s between the two types of studies. This supports the view that the endpoint for female fertility is likely to be already covered by the LOAEL derived from the chronic study and any risk for female fertility will be addressed within the risk characterisation for repeated dose toxicity and carcinogenicity.” Taking this view into consideration and for animal welfare reasons the applicant is not proposing any further studies on toxicity to reproduction at this point in time.


Short description of key information:
A negative result was obtained in a fertility study carried out in male rabbits in which animals were dosed daily with concentrations of TDCP up to 200 mg/kg/day for twelve weeks and then mated with two females during the last week of treatment. Mating, fertility, pregnancy parameters, sperm analysis and the male reproductive tract were unaffected by treatment.

Effects on developmental toxicity

Description of key information
An overall NOAEL of 100 mg/kg/day can be derived for developmental toxicity based on the statistically significant increased resorptions and the decreased foetal viability index at 400 mg/kg/day seen in the Stauffer Chemical Company developmental study reported (1978).
Link to relevant study records
Reference
Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1978
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline study, not conducted according to GLP.
Principles of method if other than guideline:
TDCP was administered daily to 20 mated Sprague Dawley female rats/dose group by oral gavage from days 6-15 of gestation
GLP compliance:
no
Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River breeding Laboratories Inc, Wilmington, MA.
- Age at study initiation: no data
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: Housed individually in a hanging wire cage with access to food and water
- Diet: ad libitum (Purina Laboratory Chow)
- Water: ad libitum
- Acclimation period: 27 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): no data
- Humidity (%): no data
- Photoperiod (hrs dark / hrs light): no data
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: Appropriate amount sof test material were mixed on a weight-per-volume basis in a vehicle of corn oil at concentrations of 12.5, 50 and 200 mg/ml


DIET PREPARATION
- Rate of preparation of diet (frequency): weekly
- Mixing appropriate amounts with (Type of food): corn oil
- Storage temperature of food: approx. 4 degrees centigrade
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Data are not available, however from the study report it was indicated that samples of each test solution (one sample taken at the time of preparation and one sample taken at the end of each dosing week - for a total of three weeks) were frozen and sent to the sponsor for analysis of the concentrations of the test material. Samples of corn oil vehicle were also sent to the sponsor.
Details on mating procedure:
Subjects are mated prior to study acceptance.
- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1/2
- Length of cohabitation: until mated
- Proof of pregnancy: sperm in vaginal smear, referred to as day 0 of pregnancy
Duration of treatment / exposure:
Subjects were treated from days 6 - 15 of gestation.
Frequency of treatment:
Daily
Duration of test:
10 days.
No. of animals per sex per dose:
20 Females per dose group and 20 females in control group.
Control animals:
yes, concurrent vehicle
Maternal examinations:
Mortalities, clinical signs, body weight, feed consumption and necropsy were carried out on adult females.
Ovaries and uterine content:
Numbers of corpora lutea, implantations, resorptions, live foetuses and dead foetuses were noted.
Fetal examinations:
One third of the foetuses were examined by serial whole body sectioning using Wilson’s technique. The remaining foetuses were eviscerated, fixed and examined for skeletal abnormalities using alizarin red staining.
Statistics:
The mean gains in maternal body weights, mean maternal food consumption values, mean ovarian, uterine and litter data and the mean fetal weights and lengths of each treated group were compared to the control group by Student's T-test when the variances of the two groups were not found to differ statistically (F significant), Cochran's approximation of t(t') was utilised. The reproduction indices of the control and treated groups were analysed by the chi-square method. All statistcial analyses were evaluated at a probability level of 0.05.
Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
There were three mortalities at the highest dose. These may have been caused by intubation errors, as findings at necropsy were not considered indicative of treatment-related effects. Clinical signs of toxicity were marked in most animals of the high dose and consisted of urine stains (19/20), hunched appearance (20/20), salivation (18/20) and alopecia (7/20). Rough coat (3/20), bloody crust around the nose (3/20), thinness (2/20) and depression (1/20) were noted in number of high dose animals also. Some clinical signs were also noted in the mid dose group and these may have been treatment-related (alopecia (1/20), hunched appearance (3/20), rough hair coat (1/20) and urine stains (5/20)). There was a significant body weight loss in mid and high dose animals from days 6-11 of treatment. These treated animals lost 15.6 g and 28.9 g, respectively, when compared to untreated animals who gained 22.1 g during this period. From days 11-15, mean weight gain of mid and low dose groups was not different from control, while mean weight gains were reduced in the 400 mg/kg/day group (50% of control). The overall mean weight gain from days 0-19 was significantly reduced (p<0.05) at 400 mg/kg/day (56% of controls). The mean weight gain in low and mid dose animals was not different to that of untreated animals. Mean food consumption was significantly reduced to 84.8% at 100 mg/kg/day (days 7-11) and at 400 mg/kg/day to an average of 45% throughout treatment. There were no specific findings at necropsy, which were indicative of a treatment-related effect.

Pregnancy rates were unaffected by treatment. The mean number of corpora lutea and implantation sites and the implantation efficiencies of the treated animals surviving to day 19 of gestation were similar to or exceeded control values.
Dose descriptor:
NOAEL
Effect level:
25 mg/kg bw/day
Basis for effect level:
other: maternal toxicity
Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
The authors considered that data for mean weight and crown-rump length from two of the 100 mg/kg/day litters should be removed, as they appeared to be of an older gestation age. When this was done, there was a slightly lower mean foetal weight (2.21 g) and crown-rump length (3.18 cm) for the 400 mg/kg/day litters when compared to controls (2.42 g and 3.35 cm) respectively, although these did not reach statistical significance. The finding of increased incidence of dilated lateral ventricles of the brain was slight and within the historical control range. There was considerable evidence of retarded skeletal development in the high dose group; incomplete ossification of intraparietal and supraoccipital, nonossified hyoid and nonossified centres in the sternebrae, nonossified centre of the sacral and caudal portions of the vertebrae, nonossified arches of the sacral vertebrae and incomplete ossification of the pubis, and nonossified centres in the metacarpels and metatarsels. Such findings are consistent with the reduced foetal weight, length and viability at this dose level and indicate developmental retardation which may be related to the maternal toxicity seen at 400 mg/kg/day. The finding of increased incidence of foetuses with angulated ribs at 400 mg/kg/day may have been related to treatment but is of unknown biological significance (no historical control data for this effect was included in the report).

Results indicated embryotoxicity in the high dose group. In this group, the rate of resorptions was statistically significantly increased when compared to controls (14.4 % compared to 6.7 %). The foetal viability index for the high dose group was statistically significantly lower than control. No increase was seen at the low or mid doses.
Dose descriptor:
NOAEL
Effect level:
100 mg/kg bw/day (nominal)
Basis for effect level:
other: This is based on the statistically significant increased resorptions and the decreased foetal viability index at 400 mg/kg/day.
Abnormalities:
not specified
Developmental effects observed:
not specified
Conclusions:
Under the conditions of this study Fyrol FR-2 produced no apparent compound-related effects when administered at a dose level of 25 mg/kg bw. Maternal toxicity, limited to adverse effects on body weight and food consumption, was evident at a dose level of 100 mg/kg bw. At the high test level of 400 mg/kg bw, signs of maternal toxicity included adverse clinical findings and dose-related effects on body weight and food consumption. In addition, there were signs of embryo- and fetotoxicity at the high test level which were not expected due to the maternal toxicity observed.
Effect on developmental toxicity: via oral route
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
100 mg/kg bw/day
Study duration:
subchronic
Species:
rat
Quality of whole database:
reliable
Additional information

In relation to developmental effects, there are no data available in humans. In a developmental study in rats, a dose of 400 mg/kg/day significantly increased the rate of resorptions compared to controls. At this high dose there was also evidence of retarded skeletal development. All of this was accompanied by significant maternal toxicity at this high dose. There was no evidence of embryotoxicity in the absence of maternal effects. The NOAEL for developmental toxicity was 100 mg/kg/day, based on the statistically significant increased resorptions and the decreased foetal viability index at 400 mg/kg/day.

In a second developmental study on rats, the highest dose of 400 mg/kg/day resulted in the deaths of 11 out of 15 of the dams with a reduction in live foetuses and a significantly high incidence of foetal deaths. No observations were noted at 200 mg/kg/day.

An overall NOAEL of 100 mg/kg/day can be derived for developmental toxicity based on the statistically significant increased resorptions and the decreased foetal viability index at 400 mg/kg/day seen in the first developmental study reported. This NOAEL is taken forward to risk characterisation in preference to the NOAEL of 200 mg/kg identified in the second study described, as only the abstract from the second study is available in English and therefore, full details of the study are not available to the Rapporteur.

Mode of Action Analysis / Human Relevance Framework

In vitro studies with TDCP point to potential impairement of neurodevelopment through different pathways,

which might point to a long-term impact on behaviour, locomotion and cognitive capacity of the offspring.

Neurodifferentation (Dishaw): Studies with neuronal PC12 cells indicated that TDCP can influence neurodevelopment by decreasing cell number and altering the neurodifferentation pathway. These observations were substantiated in early life stage zebrafish studies, were exposure at concentrations below the overt toxicity significantly altered larval swimming activity was observed (Dishaw).

HPT-axis (Wang): Altered T3/T4 balance, which can lead to distrubances during neurodevelopment.

However the neurodevelopmental rat study ( Moser) conducted to confirm these observations, was not convincing. The results of the set of different assessments of the offsprings were variable and not conclusive and are not supportive for the observations made in the in vitro studies.

Justification for classification or non-classification

The ECHA Committee for Risk Assessment in its opinion of Sept. 3 2010 proposed a harmonized classification of the substance as carcinogen category 2 (CLP) H351 or category 3 according to Dir. 67/548/EEC with R40 and S (2)-36/37. The committee reviewed carcinogenicity and reproductive toxicity data and came to the conclusion that no classification for reproductive toxicity was proposed as there is insufficient evidence for classification of TDCP as a male reproductive toxicant. Based on two developmental toxicity studies in rats the committee came to the conclusion that no classification for developmental toxicity is proposed as there was no evidence of embryotoxicity in the absence of maternal toxicity.