Tetrakis(diethyldithiocarbamato-S,S')tellurium

Endpoint summary

Description of key information

In a GLP compliant OECD 422 study, a NOAEL of 1 mg/kg bw/day was determined for systemic repeated dose toxicity.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

9 Dec 2016 to 20 Feb 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

July 2015

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Name of test material (as cited in study report): Tellurium diethyldithiocarbamate
- Batch No.: 60700109
- Date of receipt: 15 July 2016
- Date of expiration: 15 July 2018
- Purity: ≥ 99%

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage conditions: Ambient temperature (15 - 25°C)

OTHER SPECIFICS:
- Appearance: yellow powder

Species:

rat

Strain:

Wistar

Remarks:

(Crl:WI(Han))

Details on species / strain selection:

- Species selection: The rat was used because this species is considered suitable for this type of study, and is usually required by regulatory agencies.
- Strain selection: The rat was used because this species is considered suitable for this type of study, and is usually required by regulatory agencies.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: The animals were obtained from a colony maintained under specific pathogen-free (SPF) conditions at Charles River Deutschland, Sulzfeld, Germany.
- Age of the males: About 11 weeks at the start of pretreatment period and about 13 weeks at the start of exposure
- Age of the females: About 12 weeks at the start of pretreatment period and about 14 weeks at the start of exposure
- Weight at study initiation: Males: 312.6 - 397.9 g; Females: 206.5 - 242.6 g
- Housing: The animals were housed under conventional conditions in one animal room. No other test systems were housed in the same room during the study. The rats were housed in makrolon cages with a bedding of wood shavings (Lignocel, Rettenmaier & Söhne GmbH & Co, Rosenberg, Germany) and strips of paper (Enviro-dri, Shepherd Specialty Papers, Michigan, USA) and a wooden block (ABEDD, Vienna, Austria) as environmental enrichment. During the pre-treatment and pre-mating period the animals were housed four rats to a cage (separated by sex). For mating, one male and one female were housed together. Mated females were housed individually in cages, which were placed in another cage rack. After delivery, the cage containing the dam with a litter was transferred to another cage rack. The location of the dam with the litter in this cage rack was determined by the delivery date and the animal number.
- Diet: Food was provided ad libitum from the arrival of the rats until the end of the study, unless precluded by the performance of certain laboratory investigations. From their arrival, the rats receive a cereal-based (closed formula) rodent diet (VRF1 (FG)) from a commercial supplier (SDS Special Diets Services, Witham, England). The diets were given as a powder in stainless steel cans, covered by a perforated stainless steel plate to prevent spillage. The food in the cans was replaced once per week with fresh portions and topped up when necessary.
- Water: Drinking water was supplied ad libitum from the arrival of the animals until the end of the study. Each cage was supplied with domestic mains tap-water suitable for human consumption (quality guidelines according to Dutch legislation based on EC Council Directive 98/83/EC). The water was given in polypropylene bottles, which were cleaned weekly and filled as needed.
- Acclimation period: Upon arrival on 30 November 2016, the rats were taken in their unopened shipping containers to a quarantine room and were checked for overt signs of ill health and anomalies. During the quarantine period, serological investigation of the microbiological status was conducted in blood samples taken from 4 randomly selected animals of this study. On 6 December 2016, the results of the serological examinations were received. Based on the serology results the animals were accepted. The animals were subsequently released for experimental use. During the acclimatization period to the laboratory conditions and during the study, the animals were maintained in the same room.

DETAILS OF FOOD AND WATER QUALITY:
- Each batch of VRF1 (FG) diet is analysed by the supplier for nutrients and contaminants.
- Results of the routine physical, chemical and microbiological examination of drinking water as conducted by the supplier were made available to the test facility. The supplier periodically (twice per year) analyses water samples taken at the premises for a limited number of physical, chemical and microbiological variables.

ENVIRONMENTAL CONDITIONS
- Temperature: 20 - 24 °C
- Relative humidity: At least 45% and not exceeding 65% other than during short periods due to room cleaning. At some occasions, relative humidity was slightly below 45% (reaching a minimum of 29.5% on 17 January 2017) for short periods of time. This deviations were considered not to have affected the validity of the study.
- Air changes: 10 changes per hour
- Photoperiod: A sequence of 12 hours light and 12 hours dark was maintained.
- Light quality: Lighting was artificial (fluorescent tubes).

Route of administration:

oral: gavage

Details on route of administration:

The oral route of administration was used because this is an anticipated route of human exposure.

Vehicle:

corn oil

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 0.04 - 1 mg/mL
- Amount of vehicle: 5 mL/kg body weight
- Batch no.: A1600985
- Purity: 100 %

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Gavage liquid containing the test substance was destructed in the presence of sulfuric acid and hydrogen peroxide. The samples were subsequently diluted using 1.4 M HNO3 and analysed using inductively coupled plasma - mass spectrometry (ICP-MS). Rhodium was used as internal standard. The test substance was quantified using tellurium (Te) as a marker.
- Validation criteria: The acceptance criterion for linearity was as follows: the correlation coefficient of the calibration curves should be ≥ 0.996.
- Homogeneity: The homogeneity of the test substance was assessed in the batches of gavage liquids, prepared on 28 December 2016, 17 January 2017, 30 January 2017 and 13 February 2017. Three samples of each test gavage liquid, taken at different locations in the gavage liquid container, and 1 sample of the control gavage liquid were analysed in duplicate. For each concentration level, a one-way analysis of variance (Anova) was performed using the sample location (1-3) as grouping factor. An associated F-value with probability p < 0.01 was considered to be significant (i.e. the mean concentrations differ significantly at the three locations in the gavage liquid container). The test substance was considered to be homogeneously distributed in the gavage liquid if p ≥ 0.01 and/or if the relative standard deviation (RSD) between the mean concentrations at the three locations was ≤ 5%.
- Content: The content of the test substance was determined in the batches of gavage liquids, prepared on 28 December 2016, 17 January 2017, 30 January 2017 and 13 February 2017. The content of the test substance in gavage liquid was considered to be “close to intended” if the mean measured concentration was between 90 and 110% of the intended concentration.

Duration of treatment / exposure:

The test substance was administered during a pre-mating period of 2 weeks, during mating (1 week) and post-mating up to at least 28 consecutive days for male rats.
The test substance was administered during a pre-mating period of 2 weeks and during mating (1 week), gestation and lactation until (or shortly after) postnatal day 13 (PN 13) for female rats.

Frequency of treatment:

Once daily for 7 days per week

Dose / conc.:

0.2 mg/kg bw/day (actual dose received)

Remarks:

Low-dose

Dose / conc.:

1 mg/kg bw/day (actual dose received)

Remarks:

Mid-dose

Dose / conc.:

5 mg/kg bw/day (actual dose received)

Remarks:

High-dose

No. of animals per sex per dose:

12

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose rationale: The dose levels were selected in consultation with the sponsor are were based on the results of a 2-weeks dose-range finding study with the test substance in rats

Positive control:

Not applicable

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS
Each animal was observed daily in the morning hours by cage-side observations. All cages were checked again in the afternoon for dead or moribund animals. All abnormalities, signs of ill health or reactions to treatment were recorded.

DETAILED CLINICAL OBSERVATIONS
Detailed clinical examinations outside the home cage were performed on all rats of all groups prior to the first exposure and then once weekly throughout the study, up to the last week of the gestation period. In the last week of the study the detailed clinical examinations were part of the Functional Observational Battery tests (FOB) in the animals concerned. Signs noted included but were not limited to changes in skin and fur, piloerection, changes in the eyes, gait (including posture), and presence of clonic or tonic movements, stereotypies and bizarre behaviour.

BODY WEIGHT
Body weights of male and female animals were recorded just before the start of the treatment (to enable randomization) and at the start of the study (day 0). Subsequently males were weighed weekly until sacrifice. Females were weighed once per week during the pre-mating and mating period. Mated females were weighed on days 0, 7, 14 and 20 during presumed gestation (erroneously, female animals of lot 1 were weighed on GD 21) and on days 0, 4, 7 and 13 of lactation. The animals were weighed on their scheduled necropsy date in order to calculate the organ to body weight ratios.

FOOD CONSUMPTION
Food consumption was measured per cage for the same periods as the body weights were measured, except during the mating period when food intake was not registered. The results are expressed in g per animal per day.

NEUROBEHAVIOURAL EXAMINATION
In the week prior to sacrifice, Functional Observational Battery (FOB) tests and spontaneous motor activity were performed in 5 males/group after 28 days of dosing and in 5 females with a litter/group on PN day 13. For females both tests were performed after sacrifice of their pups on PN day 13.

HAEMATOLOGY:
- Time schedule for collection of blood: prior to sacrifice
- Anaesthetic used for blood collection: Yes (CO2/O2)
- Animals fasted: Yes (water was freely available)
- How many animals: all animals
- Parameters examined: hemoglobin (Hb), packed cell volume (PCV), red blood cell count (RBC), reticulocytes, total white blood cell count (WBC), differential white blood cell counts (neutrophils, lymphocytes, eosinophils, basophils, monocytes), prothrombin time and thrombocyte count. The following parameters were calculated: mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC).

CLINICAL CHEMISTRY
- Time schedule for collection of blood: prior to sacrifice
- Animals fasted: Yes (water was freely available)
- How many animals: all animals
- Parameters examined: alkaline phosphatase activity (ALP), aspartate aminotransferase activity (ASAT), alanine aminotransferase activity (ALAT), gamma glutamyl transferase activity (GGT), total protein, albumin, ratio albumin to globulin (calculated), urea, creatinine, glucose (fasting), bilirubin (total), cholesterol (total), triglycerides, phospholipids, calcium (Ca), sodium (Na), potassium (K), chloride (Cl), inorganic phosphate (PO4) and bile acids.

Sacrifice and pathology:

SACRIFICE, GROSS NECROPSY AND HISTOLOGY OF PARENTAL ANIMALS
Prior to sacrifice, all adult male and female animals were fasted overnight (water was freely available). All surviving male and female parent animals were sacrificed by exsanguination from the abdominal aorta whilst under CO2/O2 anaesthesia at necropsy and then examined grossly for pathological changes. All males were sacrificed after the mating period on 24 January 2017 (after 29 days of dosing). Dams were sacrificed, after overnight fasting, on day 14 of lactation.

GROSS PATHOLOGY
At scheduled necropsy, the organs of the parent animals were weighed (paired organs together) as soon as possible after dissection to avoid drying. A detailed scheme of the examined organs is presented in 'Any other information on materials and methods incl. tables'. Samples of the following tissues and organs of the parent animals were preserved in a neutral aqueous phosphate-buffered 4% solution of formaldehyde; except for the testes which was preserved in Bouin’s fixative. The reproductive organs and gross lesions of all adult male and female animals were preserved. In addition, a series of other organs/tissues of five adult animals/sex/group (surviving males with the lowest identification numbers in each cage; females with a litter were selected; same animals as selected for haematology and clinical chemistry) were preserved.

HISTOPATHOLOGY
Tissues for microscopic examination were embedded in paraffin wax, sectioned, and stained with haematoxylin and eosin, except for sections of the testes which were stained with PAS haematoxylin. Microscopic examination were performed on the preserved organs of all animals of the control and high-dose group. Furthermore, organs showing gross lesions of animals of all groups were microscopically examined.

Other examinations:

BLOOD SAMPLING FOR HORMONE DETERMINATIONS
During necropsy blood was taken from the aorta under CO2/O2 anaesthesia from all male and female adult animals for determination of T4 hormone levels in serum samples. In addition, blood samples were collected from the surplus pups per litter at culling on lactation day 4 (blood of all culled pups of each litter was pooled, PN 4 pups were sacrificed by decapitation for blood collection) and from two pups per litter at sacrifice on or shortly after lactation day 13 (individual, blood was collected from the heart whilst under CO2/O2 anaesthesia). This blood was collected to determine T4 hormone levels in serum samples. Samples were stored in a freezer (≤-18°C) until analysis.

Statistics:

Tests were generally performed as two-sided tests with results taken as significant where the probability of the results was p<0.05 (*) or p<0.01 (**).
- Functional observational battery: one-way analysis of variance followed by Dunnett’s multiple comparison tests (continuous data), Kruskal-Wallis non-parametric analysis of variance followed by multiple comparison tests (rank order data) or Pearson chi-square analysis (categorical data).
- Motor activity data: total distance moved: one-way analysis of variance followed by Dunnett’s multiple comparison tests; habituation of activity: repeated measures analysis of variance on time blocks (each session consists of 5 time blocks of 6 minutes each).
- Clinical pathology data (haematology, clinical chemistry) and T4 hormone data: ‘Generalized Anova/Ancova Test’ (with ‘Automatic’ as data transformation method. This test is an automatic decision tree consisting of: (1) Data preprocessing tests. First, normality of data distribution (Shapiro-Wilks test) and homogeneity of variances (Levene test) are checked (initial transformation ‘None’ [Identity]). If any of these checks fail (p<0.05) they are repeated using Log transformation. If checks on log-transformed data fail, data are rank-transformed; (2) A group test assessing whether or not group means are all equal (parametric for untransformed or log-transformed data: one-way analysis of variance [Anova]; nonparametric for rank transformed data: Kruskal-Wallis test); (3) Post-hoc analysis. If the group test shows significant (p<0.05) non-homogeneity of group means, pairwise comparisons with the control group are conducted by Dunnett’s multiple comparison test (parametric after Anova, non-parametric after Kruskal-Wallis; significance levels 0.01 and 0.05).

Clinical signs:

no effects observed

Description (incidence and severity):

There were no treatment-related clinical signs during the pre-mating period, mating period, post-mating period, gestation period or the lactation period.

Mortality:

no mortality observed

Description (incidence):

No mortalities were observed. On the first day of the mating period, one female of the control group had to be sacrificed in a moribund condition because she had a bad wound due to fighting with here male cage-mate.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

- There were no treatment-related effects on body weights and body weight changes of male and female animals during the pre-mating period and of males during the post-mating period.
- On gestation days 7, 14 and 20, body weights of the female animals of the high-dose group were statistically significantly lower than the body weights of the control animals. Body weight changes of the female animals of the high-dose group were statistically significantly lower from gestation day 7-14, 14-20 and 0-20.
- During the lactation period, body weights of the females of the high-dose group were statistically significantly lower than the body weights of the control animals whereas no statistically significant effects were observed on body weight changes.
- Terminal body weights of male and female animals of the high-dose group were statistically significantly lower than of the male and female animals of the control group.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

- There were no treatment-related effects on food consumption of male and female animals during the pre-mating period and of males during the post-mating period.
- During the gestation period (GD 7-14 and 14-20), food consumption of the females of the high-dose group was statistically significantly lower than the food consumption of the control animals.
- During the lactation period, in the mid-dose group food consumption was statistically significantly decreased between postnatal days 4 to 7. No other statistically significant effects were observed on food consumption during the lactation period.

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

- In male and female animals no differences in red blood cell and coagulation parameters were observed among the control and the treatment groups.
- As compared to the control group, in male animals of the low-dose group statistically significant lower values were observed for the number of white blood cells, the absolute number of lymphocytes and on the absolute- and relative numbers of basophiles. Since no differences were observed on total and differential white blood cell parameters in male animals of the mid- and high-dose groups nor in the female animals of all treatment groups, the effects observed in the male animals of the low-dose group were considered as chance findings and not related to treatment.
- In conclusion, there were no treatment-related changes in red blood cell and coagulation parameters and in total and differential white blood cell counts.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

- Except for two incidental findings (statistically significant higher concentrations of ALP in the low-dose group and of potassium in the high-dose group) in male animals, no differences were observed in clinical chemistry parameters among the control and treatment groups.
- In female animals, the concentration of cholesterol in the high-dose group was statistically significantly higher than in control animals.
- In conclusion, except for some incidental findings which were considered chance findings and not related to treatment, no effects on clinical chemistry parameters were observed.

Urinalysis findings:

not examined

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

- The mean landing footsplay of male animals of the high-dose group was statistically significantly increased in comparison to the control group. Also, the time pattern of activity of males of both the mid-and high-dose groups were significantly different when compared to control males. These findings might reflect a neurotoxic effect of the test substance.
- No other effects were observed in male and female animals.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

- In male and female animals, no statistically significant differences were observed in the mean absolute organ weights between the control and treatment groups.
- The relative liver weight of male animals of the mid- and high-dose groups (8% and 13%, respectively) and the relative kidney weight of the high-dose males (9%) were statistically significantly increased as compared to the control group.
- In female animals of the high-dose group, the relative weights of the brain (15%), liver (12%) and kidneys (12%) were statistically significantly increased as compared to control animals.
- The effects on organ weights of >10% as observed in male- and female animals of the high-dose group were considered as treatment related.

Gross pathological findings:

no effects observed

Description (incidence and severity):

Macroscopic observations at necropsy revealed no treatment-related abnormalities. The findings were unremarkable and part of the background pathology of rats of this strain and age.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

Microscopic examinations revealed no treatment-related abnormalities. The histopathological findings were considered unremarkable and part of the background pathology of rats of this strain and age.

Histopathological findings: neoplastic:

no effects observed

Other effects:

no effects observed

Description (incidence and severity):

HORMONE ANALYSIS
No statistically significant effects were observed amongst the different groups.

Key result

Dose descriptor:

NOAEL

Effect level:

1 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

behaviour (functional findings)

body weight and weight gain

food consumption and compound intake

organ weights and organ / body weight ratios

Key result

Critical effects observed:

no

ANALYTICAL VERIFICATION OF DOSES OR CONCENTRATIONS

- Linearity: The correlation coefficient was 1.000 during the 6 runs which were performed during this study and therefore the preset criterion was met.

- Homogeneity: The RSD between the mean concentrations at three different locations was < 5% and/or p was ≥ 0.01 for all dose levels of all tested batches. Therefore the test substance was considered to be homogeneously distributed in the gavage liquids. However, the RSD for the low-dose gavage liquid prepared on 17 January 2017 was extremely high (60%), which raises serious questions about the homogeneity of the low-level gavage liquid of this batch.

- Content: The concentration of the test substance was close to intended (90-110%) for all gavage liquids at all dose levels, except for the low-dose level of the gavage liquids prepared on 17 January 2017 (+52%) and 30 January 2017 (-24%) and the mid-dose level of the gavage liquids prepared on 30 January 2017 (-12%). Because the average deviation from the intended concentration was less than 10% for each dose level when all 4 batches are considered, it was assumed that, on average, the animals received the intended test substance dose during the study.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

1 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

GLP compliant OECD 422 study

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In a GLP-compliant repeated dose toxicity study performed according to OECD guideline 422, the test substance formulated in corn oil, was administered daily by oral gavage to male and female Wistar rats at dose levels of 0.2, 1 and 5 mg/kg bw/day (12 rats/sex/dose level) (Triskelion B.V., 2018). The dose levels were based on a dose-range finding study performed previously. Concurrent controls (12 rats/sex) received the vehicle only. The test substance was administered during a pre-mating period of 2 weeks, during mating (1 week) and post-mating up to at least 28 consecutive days for male rats and during a pre-mating period of 2 weeks and during mating (1 week), gestation and lactation until (or shortly after) postnatal day 13 (PN 13) for female rats. The following observations and examinations were evaluated: mortality / viability, clinical signs (daily), (neuro-)functional observations (end of treatment), body weight and food consumption (at least at weekly intervals), macroscopy at termination, haematology (end of treatment), clinical chemistry (end of treatment) and hormone determination (end of treatment). Organ weights were determined of adrenal glands [paired], Brain [including sections of cerebrum, cerebellum, medulla/pons], Heart, Kidney, Liver, Lungs with trachea and larynx [paired], Spleen, Thymus, Thyroid gland. Additionally, histopathology was performed on these tissues and on all gross lesions, Bone marrow ([femur], Eye, Mesenterial and axillary lymph nodes, Peripheral nerve [sciatic or tibial], Pituitary, Small and large intestines [including Peyer’s pathes], Spinal cord, Stomach, Skeletal muscle [thigh] and Urinary bladder. Linearity, homogeneity and content of formulations were demonstrated by analyses. The results of test substance analysis in the carrier showed that, on average, the test substance was homogenously distributed in the carrier and that the concentrations of the test substances in the carrier were close to intended. No clinical signs or mortality were observed throughout the study. Significant treatment-related body weight changes were observed (decrease) in females during the gestation and lactation period in the high-dose group. Food consumption in the gestation period was also significantly decreased in females in the high-dose group. No haematological, histopathological, hormonal or clinical chemistry findings were observed. However, the mean landing footsplay of male animals of the high-dose group was statistically significantly increased in comparison to the control group. Also, the time pattern of activity of males of both the mid-and high-dose groups were significantly different when compared to control males. Although these effects represents no clear neurotoxic effects, these findings were considered to be related to treatment. Treatment related effects were observed on relative organ weight in the high-dose group for males in the liver and for females in the brain, liver and kidneys (≥10% increase). Based on the results, the NOAEL for systemic toxicity was determined to be 1 mg/kg bw/day.

Justification for classification or non-classification

Based on the available data, classification for repeated dose toxicity is not warranted according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.