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Effects on fertility

Description of key information

The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.

Link to relevant study records
Reference
Endpoint:
screening for reproductive / developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study conducted on read across material
Justification for type of information:
Read-across test result from source substance MMTC to target substance MMT(EHTG).
This data requirement is fulfilled by read-across. Justification for the read-across of this test result is provided in Section 7.1 Toxicokinetics. The simulated gastric hydrolysis study shows rapid and complete conversion of MMT(EHTG) to MMTC. Based on this result MMTC fulfils the requirements of being a source compound for studies required for MMT(EHTG) where the endpoint is based on oral exposure. The study on MMTC can be applied both quantitatively and qualitatively for the end point for MMT(EHTG).
Reason / purpose:
other: Read across target
Reason / purpose:
read-across: supporting information
Qualifier:
according to
Guideline:
OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)
Deviations:
no
Principles of method if other than guideline:
The toxicity of trichloromethylstannane [CAS # 993-16-8] in Wistar rats was examined using continuous administration via the diet for 13 consecutive weeks (OECD Test Guideline 408). In satellite groups of female rats a reproduction/developmental screening test (OECD Test Guideline 421) was performed to provide initial data on possible reproductive and developmental effects of trichloromethylstannane.

The method of analysis involved derivatisation. This method only measures the amount of the alkyltin moiety, MMT, present and does not identify the other ligands attached to the tin. Currently there is no analytical method available that can quantify the actual named substance, i.e., the entire organotin compound with its associated chloride ligand.
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
Wistar
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany.
- Age at study initiation: (P) 15-16 weeks
- Weight at study initiation: (P) Males: 113.9 - 13.8 g (mean 126.3g); Females: 178.8 - 213.5 g (mean 199.7 g)
- Fasting period before study: not reported
- Housing: 3 or 4 per group per cage; during gestation and lactation they were housed individually
- Use of restrainers for preventing ingestion (if dermal): not applicable
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 13 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3 °C
- Humidity (%): 30 % not exceeding 70 %
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12 hours light/ 12 hours dark

IN-LIFE DATES: From: May 20, 2003 To: June 26- July 14, 2003
Route of administration:
oral: feed
Vehicle:
unchanged (no vehicle)
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: The test substance was incorporated into the basal diet by mixing in a mechanial blender

DIET PREPARATION
- Rate of preparation of diet (frequency): shortly before the start of the studies and every 6 weeks thereafter
- Mixing appropriate amounts with (Type of food): Rat and Mouse No. 3 Breeding Diet, RM3
- Storage temperature of food: stored in a freezer until use

VEHICLE- no vehicle
Details on mating procedure:
- M/F ratio per cage: 1:1
- Length of cohabitation: During the mating period one male and one female of the same dose group were caged until copulation occurred or two weeks had elapsed.
- Proof of pregnancy: The day a vaginal smear was detected sperm positive was considered gestation day 0. During the mating period every consecutive morning vaginal smears were made to ascertain copulation by detection of sperm cells in the smear.
- After unsuccessful pairing, replacement of first male by another male with proven fertility: Yes. If a male died before or during the mating period before the female was found sperm positive, the female was mated with another, proven male of the same group (i.e. a male which already had a successful copulation, sperm positive smear with another female).
- After successful mating each pregnant female was caged (how): During the premating period females were housed 3 or 4 per group per cage. Male rats of the 13 week study were mated after a premating period of 10 weeks with the female rats. During the gestation and lactation periods the females were housed individually.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
ANALYTICAL METHODS: GC-MS was used to determine the achieved concentration, homogeneous distribution and stability of the test substance in diet samples. The method of analysis involved derivatisation. This method only measures the amount of the alkyltin moiety, MMT, present and does not identify the other ligands attached to the tin. Currently there is no analytical method available that can quantify the actual named substance, i.e., the entire organotin compound with its associated chloride ligand.
From each diet sample, 2.0 g was transferred into a 50 mL Greiner tube. An aliquot of the internal standard solution was added. Subsequently, methanol, acetate buffer solution, 20 % aqueous NaBEt4 solution and hexane were added to each sample and this mixture was shaken and heated to 60 °C. Prior to GC/MS analysis, the hexane layer was washed with 2 mol/L HCl in order to remove the ethylboron compounds. The concentration of each test substance in feed was determined by GC-MS analysis of the hexane extracts.

Analysis of the test substance in diet samples revealed that the test substance dose was close to the nominal level for all diets. Mean measured concentrations ranged from 96 to 113 % of nominal concentrations. Homogeneity: The test substance was considered to be homogenously distributed in all diets. Stability: The test substance was considered to be stable in the diets upon storage at room temperature for 7 days and upon storage at < -18 °C for 6 weeks.
Duration of treatment / exposure:
13 week study; treated for 2 consecutive weeks during the pre-mating period, daily during gestation (up to 26 days) and up to euthanasia at or shortly after postnatal day (PN) 4.
Frequency of treatment:
daily
Dose / conc.:
30 mg/kg diet
Dose / conc.:
150 mg/kg diet
Dose / conc.:
750 mg/kg diet
No. of animals per sex per dose:
10 females per dose level for satellite group
Control animals:
yes, concurrent no treatment
Details on study design:
The test substance was administered at constant concentrations in the diet for 13 consecutive weeks. The test substance was administered via the diet two weeks premating, during gestation and up to euthanasia at or shortly after postnatal day 4.
Parental animals: Observations and examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Clinical signs and mortality were observed at least once daily (in the morning) and on working days also once in the afternoon.

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: Once during the acclimatisation period, once at initiation of the study prior to introduction of feed. The females of the satellite groups were weighed 4 days before gestation, on gestation days 0, 7, 14 and 21 and on postnatal days 1 and 4. Furthermore, all animals were weighed on the day of necropsy in order to determine their correct organ to body weight ratios.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Measured per cage over weekly periods by weighing the feeders (in g/animal/day).

WATER CONSUMPTION: No
Sperm parameters (parental animals):
Parameters examined in P male parental generations: The reproductive organs of the males of the 30 and 150 mg/kg groups that failed to sire (did not mate or female was not pregnant) were microscopically examined.
Litter observations:
At the end of the gestation period, females were examined twice daily for signs of parturition. The litters were examined only daily for dead pups. The total litter size and numbers of each sex as well as the number of stillbirths, live and dead pups and grossly malformed pups were evaluated on days 1 and 4 of lactation. Mean pup weights were calculated as litter weight/number pups. The number of runts (< 2 sd from the litter mean) were noted and reported as well.
Postmortem examinations (parental animals):
GROSS NECROPSY
Organs weighed included ovaries, uterus (after counting of the implantation sites), thymus and all gross lesions.

HISTOPATHOLOGY / ORGAN WEIGHTS
Microscopic examination of the ovaries, uterus and thymus of the control and 750 mg/kg groups was performed. Examination was extended to the thymus of the females of the 30 and 150 mg/kg groups because of the effects observed in the 750 mg/kg group for this tissue/organ. Furthermore, the reproductive organs of the males of the 30 and 150 mg/kg groups that failed to sire (did not mate or female was not pregnant) and the reproductive organs of females of the 30 and 150 mg/kg groups that were non-mated or non-pregnant were microscopically examined.
Postmortem examinations (offspring):
SACRIFICE
Pups were killed by hypothermia at < -18 °C.

GROSS NECROPSY
A necropsy was performed on stillborn pups and pups dying during the study; pups were examined externally for gross abnormalities and macroscopic abnormalities were recorded.
Statistics:
- Test substance analysis: Homogeneity: one way analysis of variance (Anova) using the sample location (1-5) as grouping factor. The test substance was considered to be homogeneously distributed in the diets if p > 0.01 and/or if the relative standard deviation (RSD) between the sample means was less than or equal to 15 %. Stability: one way analysis of variance (Anova) using time as grouping factor. The test substance was considered to be stable in the diets if p > 0.01 and/or if the mean concentration on the last day was between 80 and 120 % of the mean concentration on the first day (t =0). Achieved concentration: for each concentration level, the mean of the concentrations, as measured in the diet samples used for the assessment of the homogeneity, was considered to represent the achieved concentration. The content of the test substance in the diet was considered to be 'close to intended' if the mean measured concentration was between 80 and 120 % of the intended concentration.
- Body weight: one way analysis of covariance (covariate: body weight on day 0) followed by Dunnett's multiple comparison tests.
- Food consumption and food efficiency: one way analysis of variance (Anova) followed by L.S.D. tests.
- Fisher's exact probability test was used to evaluate the number of mated and pregnant females and females with live pups. Numbers of implantation sites and live and dead pups were evaluated by Kruskal-Wallis non-parametric analysis of variance followed by the Mann-Whitney U-test.
- The litter was used as the statistical unit for calculation of foetal values.
- Histopathological changes: Fisher's exact probability test. All tests were two-sided. Probability values of p<0.05 were considered significant.
Reproductive indices:
With regard to fertility and reproductive performance, the following parameters were calculated:
-Pre-coital time = time between the start of mating and successful copulation
- Duration of gestation = time between gestation day 0 and day of delivery
- Mating index = (number of females mated/number of females placed with males) x 100
- Male fertility index = (number of males that became sires/number of males placed with females) x 100
- Female fertility index = (number of pregnant females/number of females placed with males) x 100
- Female fecundity index = (number of pregnant females/number of females mated) x 100
- Gestation index = (number of females with live pups/number of females pregnant) x 100
- Number of lost implantations = number of implantations sites - number of pups born alive
- Post-implantation loss = [(number of implantation sites - number of pups born alive)/number of implantation sites] x 100
Offspring viability indices:
- Live birth index = (number of pups born alive/number of pups born) x 100
- Pup mortality day n = (number of dead pups on day n/total number of pups on day n) x 100
- Viability index day 1-4 = (number of pups surviving 4 days/total number of live pups on day 1) x 100
- Sex ratio day n = (number of male pups on day n/ total number of pups) x 100
Clinical signs:
not specified
Mortality:
mortality observed, treatment-related
Description (incidence):
One animal of the 750 mg/kg group was found dead on GD 22 (i.e. 37 days after the start of exposure).
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
An increased body weight change from GD 7-14 of the females of the 30 mg/kg group was noted, which was considered a chance finding. Mean body weights (change) of the females were similar among the control, 30 and 150 mg/kg group during the entire study. Mean body weight (changes) between PN 1-4 of the 750 mg/kg group was decreased; however, no statistical significance was reached for these findings.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
Food consumption of the female animals of the 750 mg/kg group was decreased (not statistically significantly) during the lactation period. During the premating and gestation periods food consumption of the females was similar in the control, 30, 150 and 750 mg/kg groups.

The test substance intake of the female animals of the 30, 150 and 750 mg/kg dose groups was respectively:
- Premating period days 0-7: 1.8, 9.0 and 44.5 mg/kg bw/day
- Premating period days 7-14: 1.8, 8.8 and 43.9 mg/kg bw/day
- Gestation period GD 0-7: 1.9, 9.6 and 44.5 mg/kg bw/day
- Gestation period GD 7-14: 2.0, 9.6 and 45.8 mg/kg bw/day
- Gestation period GD 14-21: 1.2, 6.2 and 35.9 mg/kg bw/day
- Lactation period PN 1-4: 1.7, 11.7 and 26.5 mg/kg bw/day
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not specified
Haematological findings:
not specified
Clinical biochemistry findings:
not specified
Urinalysis findings:
not specified
Behaviour (functional findings):
not specified
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Description (incidence and severity):
Mean absolute and relative uterus, ovary and thymus weights were similar in all groups.
Gross pathological findings:
effects observed, non-treatment-related
Description (incidence and severity):
No treatment related changes were observed. The animal found dead on day 37 was necropsied. Findings included yellow patches on the liver, yellow appearance of the small intestines, haemorrhagic discharge from the vagina and a haemothorax. The haemothorax was considered to be the probable cause of death. Most probably the haemothorax was caused by severe dystocia, since at necropsy the uterus contained 12 dead foetuses.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
no effects observed
Description (incidence and severity):
No treatment related histopathological changes were observed in the uterus, ovary and thymus of the female animals of the control and 750 mg/kg groups.
Histopathological findings: neoplastic:
not examined
Reproductive function: oestrous cycle:
not examined
Reproductive function: sperm measures:
not examined
Reproductive performance:
effects observed, treatment-related
Description (incidence and severity):
- Pre-coital time: comparable among the control and the treated groups.
- Mating index: 90 -100 %
- Number of pregnant females per dose level: 9, 8, 9 and 8 for the control, 30, 150 and 750 mg/kg groups, respectively.
- Female fecundity index: comparable among the control and the treated groups.
- Female fertility index: comparable among the control and the treated groups.
- Male fertility index: comparable among the control and the treated groups.
- Number aborting: No data available
- Number of resorptions: No data available
- Mean number of implantations: 11.2 (control group), 10.8 (30 mg/kg), 11.6 (150 mg/kg), 10.5 (750 mg/kg).
- Gestation index: 89, 100, 100 and 88 % in the control, 30, 150 and 750 mg/kg groups, respectively.
- Live birth index: 98, 97, 100 and 96 % in the control, 30, 150 and 750 mg/kg groups, respectively.
- Number of pups born (number of litters): 90 (8), 86 (8), 99 (9) and 50 (7) for the control, 30, 150 and 750 mg/kg groups, respectively.
- Number of stillborn pups (number of litters): 2 (1), 3 (2), 0 and 2 (2) for the control, 30, 150 and 750 mg/kg groups, respectively.
- Post implantation losses [total implantation sites minus total live births at the first observation]: 13 (18.6 %), 16 (15.3 %), 5 (4.7 %) and 36 (42.9 %) for the control, 30, 150 and 750 mg/kg groups, respectively. Interpretation of these data was complicated by the incidence of missing pups across groups. A variable incidence of pups "missing" after birth was recorded. The incidence of missing pups was statistically significantly higher than controls in the high-dose group, statistically significantly lower than controls in the mid-dose group, and not statistically different than controls in the low-dose group. The missing pups were presumed to have been cannibalised by the dams, but it is not known if the missing pups were alive or dead. It is also not known if some pups were cannibalised prior to being counted for litter size. This could account for the slightly lower number of recorded live births and the slightly higher post-implantation loss in the high-dose versus controls. The reason for missing pups cannot be determined on the basis of the data within the study. Missing pups could be due solely to a toxic behavioural effect on dams which caused a lack of, or abnormal, nurturing. It is clear that no malformations were noted at any observation point for any of the missing pups and no overt behavioural effects were noted; however some other effect could have caused the dam to eat them.
- Number of corpora lutea: No data available
- Duration of Pregnancy: 21 -23 days
Key result
Dose descriptor:
NOAEL
Remarks:
fertility and developmental effects
Effect level:
150 mg/kg diet
Based on:
test mat.
Sex:
male/female
Basis for effect level:
reproductive performance
Key result
Dose descriptor:
NOAEL
Remarks:
maternal toxicity
Effect level:
150 mg/kg diet
Based on:
test mat.
Sex:
female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
other: 150 mg/kg diet (equivalent to 6.2 - 11.7 mg/kg bw/day in females) was considered to be the NOAEL for maternal toxicity.
Mortality / viability:
mortality observed, treatment-related
Description (incidence and severity):
- Pup mortality: 2.2, 3.5, 0 and 4 % for the control, 30, 150 and 750 mg/kg groups, respectively (PN 1); 16, 25, 3 and 65 % for the control, 30, 150 and 750 mg/kg groups, respectively (PN 4).
- Number viable: The viability index (PN 1-4) was 84, 75, 97 and 35 % in the control, 30, 150 and 750 mg/kg groups, respectively.
- Number live pups per litter: 11.0, 10.4, 11.0 and 6.9 for the control, 30, 150 and 750 mg/kg groups, respectively (PN 1); 10.6, 7.8, 10.7 and 4.2 for the control, 30, 150 and 750 mg/kg groups, respectively (PN 4).
Body weight and weight changes:
no effects observed
Description (incidence and severity):
- Litter weight: The mean pup weights and pup weight changes were similar in the treated groups when compared to the control group.
Gross pathological findings:
effects observed, non-treatment-related
Description (incidence and severity):
- Grossly visible abnormalities: In the 30 mg/kg group, the number of cold pups was statistically significantly increased on PN 1 and 4. In addition on PN 4, the number of runts, pale pups and pups with no milk in the stomach was statistically significantly increased in the 30 mg/kg group. In the 150 mg/kg group the number of pale pups on PN 4 was statistically significantly increased. In the 750 mg/kg group the number of cold pups was statistically significantly increased on PN 1. As most effects were observed in the 30 mg/kg group only, these effects were not considered to be treatment related. Macroscopic observation of the stillborn pups revealed no abnormalities of the pups.
Other effects:
effects observed, treatment-related
Description (incidence and severity):
- Litter size: The mean number of pups delivered per litter amounted to 11.2, 10.8, 11.0 and 7.1 for the control, 30, 150 and 750 mg/kg groups, respectively.
- Sex ratio: No difference was observed in the sex ratio between the groups.
Key result
Dose descriptor:
NOAEL
Remarks:
postnatal toxicity
Generation:
F1
Effect level:
150 mg/kg diet
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: Based on the incidences of missing pups in the 750 mg/kg group, 150 mg/kg can be considered as a NOAEL for postnatal toxicity.
Key result
Reproductive effects observed:
yes
Lowest effective dose / conc.:
750 mg/kg diet
Treatment related:
yes
Relation to other toxic effects:
not specified
Dose response relationship:
no
Relevant for humans:
not specified
Conclusions:
The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.
Executive summary:

The toxicity of trichloromethylstannane [CAS # 993-16-8] in Wistar rats was examined using continuous administration via the diet for 13 consecutive weeks (OECD Test Guideline 408). In satellite groups of female rats a reproduction/developmental screening test (OECD Test Guideline 421) was performed to provide initial data on possible reproductive and developmental effects of trichloromethylstannane. The main study used four groups of 10 rats/sex (13 -week study) and the satellite study used four groups of 10 female rats (reproduction/developmental screening study). For both studies the control group was kept on control diet and three test groups received experimental diets containing 30, 150 and 750 mg/kg [ppm] of the test substance. The dose levels used in both studies were based on the results of a preceding dose range finding study.

In the satellite study female rats were fed their respective test diets beginning 2 weeks prior to the mating period, and continued on test diets through mating, gestation, and up to PN 4 or shortly thereafter. Male rats from the main study were mated after a premating period of 10 weeks with female rats of the satellite groups which were fed the same dose of test diets.

Clinical observations, growth, food consumption, food conversion efficiency, neurobehavioural testing, ophthalmoscopy, haematology, clinical chemistry, renal concentration test, urinalysis, organ weights and gross examination at necropsy, microscopic examination of various organs and tissues and assessment of various reproductive and developmental parameters were used as criteria for detecting the effects of treatment. 

The calculated doses during the pre-mating, gestation and lactation periods for the females receiving 30, 150, or 750 mg/kg trichloromethylstannane in the diet ranged from 1.2-2.0, 6.2-11.7 and 26.5-45.8 mg/kg body weight, respectively.

During the study one animal of the 750 mg/kg group was found dead on GD22. Most probably haemothorax caused by dystocia was the cause of death. No other mortalities or treatment-related clinical signs were observed in the female animals of the satellite groups.

Mean body weight, body weight change and food consumption was similar in the control and the 30 and 150 mg/kg groups. Mean body weight on PN 4 and mean body weight change PN 1-4 of the 750 mg/kg group was decreased, although not statistically significantly.

During the premating and gestation periods, mean food consumption of the female animals was similar in the control, 30 and 150 mg/kg groups. During the lactation period food consumption of the 750 mg/kg group was decreased (not statistically significantly).

No treatment-related effects on reproduction and development of the pups were observed in the 30 and 150 mg/kg groups.

In the 750 mg/kg group, a number of changes were seen indicative of a reproductive and developmental effect. One animal was found dead on GD22 (death was most probably caused by haemothorax caused by dystocia), post-implantation loss was 43 %, the number of pups delivered was 7.1 versus 11.2 in the control group, 3 females lost all pups between PN 1-4, and pup mortality between PN 1-4 in the 750 mg/kg group was 65 versus 16 % in the control group.

No treatment-related effects on pup weight and pup abnormalities were observed.

Absolute and relative organ weights (uterus, ovary and thymus) were similar among the groups. At microscopic examination of these organs no treatment-related histopathological changes were observed.

Based on reproductive and developmental effects (decreased number of pups delivered and increased post implantation loss and pup mortality) observed after mating of female animals of the 750 mg/kg satellite group with male animals of the main study, the mid-dose level 150 mg Trichloromethylstannane/kg diet (equivalent to 9.8 mg/ kg body weight/day in males and 6.2-11.7 mg/kg body weight for females) can be considered as a NOAEL for fertility and developmental effects.

Based on the effects on body weight and food consumption in the 750 mg/kg group, 150 mg Trichloromethylstannanel kg diet (equivalent to 6.2-11.7 mg/kg body weight/day) can be considered as a NOAEL for maternal toxicity.

The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.

Effect on fertility: via oral route
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
6.2 mg/kg bw/day
Study duration:
subacute
Species:
rat
Quality of whole database:
A single screening study conducted in accordance with standardised guidelines under GLP conditions on a read across substance is available. The quality of the database is therefore considered to be adequate.
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 toxicity of trichloromethylstannane [CAS # 993-16-8] in Wistar rats was examined using continuous administration via the diet for 13 consecutive weeks (OECD Test Guideline 408). In satellite groups of female rats a reproduction/developmental screening test (OECD Test Guideline 421) was performed to provide initial data on possible reproductive and developmental effects of trichloromethylstannane. The main study used four groups of 10 rats/sex (13 -week study) and the satellite study used four groups of 10 female rats (reproduction/developmental screening study). For both studies the control group was kept on control diet and three test groups received experimental diets containing 30, 150 and 750 mg/kg [ppm] of the test substance. The dose levels used in both studies were based on the results of a preceding dose range finding study.

In the satellite study female rats were fed their respective test diets beginning 2 weeks prior to the mating period, and continued on test diets through mating, gestation, and up to PN 4 or shortly thereafter. Male rats from the main study were mated after a premating period of 10 weeks with female rats of the satellite groups which were fed the same dose of test diets.

Clinical observations, growth, food consumption, food conversion efficiency, neurobehavioural testing, ophthalmoscopy, haematology, clinical chemistry, renal concentration test, urinalysis, organ weights and gross examination at necropsy, microscopic examination of various organs and tissues and assessment of various reproductive and developmental parameters were used as criteria for detecting the effects of treatment. 

The calculated doses during the pre-mating, gestation and lactation periods for the females receiving 30, 150, or 750 mg/kg trichloromethylstannane in the diet ranged from 1.2-2.0, 6.2-11.7 and 26.5-45.8 mg/kg body weight, respectively.

During the study one animal of the 750 mg/kg group was found dead on GD22. Most probably haemothorax caused by dystocia was the cause of death. No other mortalities or treatment-related clinical signs were observed in the female animals of the satellite groups.

Mean body weight, body weight change and food consumption was similar in the control and the 30 and 150 mg/kg groups. Mean body weight on PN 4 and mean body weight change PN 1-4 of the 750 mg/kg group was decreased, although not statistically significantly.

During the premating and gestation periods, mean food consumption of the female animals was similar in the control, 30 and 150 mg/kg groups. During the lactation period food consumption of the 750 mg/kg group was decreased (not statistically significantly).

No treatment-related effects on reproduction and development of the pups were observed in the 30 and 150 mg/kg groups.

In the 750 mg/kg group, a number of changes were seen indicative of a reproductive and developmental effect. One animal was found dead on GD22 (death was most probably caused by haemothorax caused by dystocia), post-implantation loss was 43 %, the number of pups delivered was 7.1 versus 11.2 in the control group, 3 females lost all pups between PN 1-4, and pup mortality between PN 1-4 in the 750 mg/kg group was 65 versus 16 % in the control group.

No treatment-related effects on pup weight and pup abnormalities were observed.

Absolute and relative organ weights (uterus, ovary and thymus) were similar among the groups. At microscopic examination of these organs no treatment-related histopathological changes were observed.

Based on reproductive and developmental effects (decreased number of pups delivered and increased post implantation loss and pup mortality) observed after mating of female animals of the 750 mg/kg satellite group with male animals of the main study, the mid-dose level 150 mg Trichloromethylstannane/kg diet (equivalent to 9.8 mg/ kg body weight/day in males and 6.2-11.7 mg/kg body weight for females) can be considered as a NOAEL for fertility and developmental effects.

Based on the effects on body weight and food consumption in the 750 mg/kg group, 150 mg Trichloromethylstannanel kg diet (equivalent to 6.2-11.7 mg/kg body weight/day) can be considered as a NOAEL for maternal toxicity.

The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.

Effects on developmental toxicity

Description of key information

In a reproduction/developmental screening study following the OECD 421 guideline the NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.

In two Developmental Neurotoxicity (DNT) studies conducted by Moser, the results indicate that perinatal exposure to the test substance, even at concentrations which decrease maternal fluid intake, does not result in significant neurobehavioral or cognitive deficits.

Link to relevant study records

Referenceopen allclose all

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted on read across material
Justification for type of information:
Read-across test result from source substance MMTC to target substance MMT(EHTG).
This data requirement is fulfilled by read-across. Justification for the read-across of this test result is provided in Section 7.1 Toxicokinetics. The simulated gastric hydrolysis study shows rapid and complete conversion of MMT(EHTG) to MMTC. Based on this result MMTC fulfils the requirements of being a source compound for studies required for MMT(EHTG) where the endpoint is based on oral exposure. The study on MMTC can be applied both quantitatively and qualitatively for the end point for MMT(EHTG).
Reason / purpose:
other: Read across target
Reason / purpose:
read-across: supporting information
Qualifier:
according to
Guideline:
other: OECD 421
Principles of method if other than guideline:
The toxicity of trichloromethylstannane [CAS # 993-16-8] in Wistar rats was examined using continuous administration via the diet for 13 consecutive weeks (OECD Test Guideline 408). In satellite groups of female rats a reproduction/developmental screening test (OECD Test Guideline 421) was performed to provide initial data on possible reproductive and developmental effects of trichloromethylstannane.

The method of analysis involved derivatisation. This method only measures the amount of the alkyltin moiety, MMT, present and does not identify the other ligands attached to the tin. Currently there is no analytical method available that can quantify the actual named substance, i.e., the entire organotin compound with its associated chloride ligand.
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
Wistar
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany.
- Age at study initiation: (P) 15-16 weeks
- Weight at study initiation: (P) Males: 113.9 - 13.8 g (mean 126.3g); Females: 178.8 - 213.5 g (mean 199.7 g)
- Fasting period before study: not reported
- Housing: 3 or 4 per group per cage; during gestation and lactation they were housed individually
- Use of restrainers for preventing ingestion (if dermal): not applicable
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 13 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3 °C
- Humidity (%): 30 % not exceeding 70 %
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12 hours light/ 12 hours dark

IN-LIFE DATES: From: May 20, 2003 To: June 26- July 14, 2003
Route of administration:
oral: feed
Vehicle:
unchanged (no vehicle)
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: The test substance was incorporated into the basal diet by mixing in a mechanial blender

DIET PREPARATION
- Rate of preparation of diet (frequency): shortly before the start of the studies and every 6 weeks thereafter
- Mixing appropriate amounts with (Type of food): Rat and Mouse No. 3 Breeding Diet, RM3
- Storage temperature of food: stored in a freezer until use

VEHICLE- no vehicle
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
ANALYTICAL METHODS: GC-MS was used to determine the achieved concentration, homogeneous distribution and stability of the test substance in diet samples. The method of analysis involved derivatisation. This method only measures the amount of the alkyltin moiety, MMT, present and does not identify the other ligands attached to the tin. Currently there is no analytical method available that can quantify the actual named substance, i.e., the entire organotin compound with its associated chloride ligand.
From each diet sample, 2.0 g was transferred into a 50 mL Greiner tube. An aliquot of the internal standard solution was added. Subsequently, methanol, acetate buffer solution, 20 % aqueous NaBEt4 solution and hexane were added to each sample and this mixture was shaken and heated to 60 °C. Prior to GC/MS analysis, the hexane layer was washed with 2 mol/L HCl in order to remove the ethylboron compounds. The concentration of each test substance in feed was determined by GC-MS analysis of the hexane extracts.

Analysis of the test substance in diet samples revealed that the test substance dose was close to the nominal level for all diets. Mean measured concentrations ranged from 96 to 113 % of nominal concentrations. Homogeneity: The test substance was considered to be homogenously distributed in all diets. Stability: The test substance was considered to be stable in the diets upon storage at room temperature for 7 days and upon storage at < -18 °C for 6 weeks.
Details on mating procedure:
- M/F ratio per cage: 1:1
- Length of cohabitation: During the mating period one male and one female of the same dose group were caged until copulation occurred or two weeks had elapsed.
- Proof of pregnancy: The day a vaginal smear was detected sperm positive was considered gestation day 0. During the mating period every consecutive morning vaginal smears were made to ascertain copulation by detection of sperm cells in the smear.
- After unsuccessful pairing, replacement of first male by another male with proven fertility: Yes. If a male died before or during the mating period before the female was found sperm positive, the female was mated with another, proven male of the same group (i.e. a male which already had a successful copulation, sperm positive smear with another female).
- After successful mating each pregnant female was caged (how): During the premating period females were housed 3 or 4 per group per cage. Male rats of the 13 week study were mated after a premating period of 10 weeks with the female rats. During the gestation and lactation periods the females were housed individually.
Duration of treatment / exposure:
13 week study; treated for 2 consecutive weeks during the pre-mating period, daily during gestation (up to 26 days) and up to euthanasia at or shortly after postnatal day (PN) 4.
Frequency of treatment:
daily
Dose / conc.:
30 mg/kg diet
Dose / conc.:
150 mg/kg diet
Dose / conc.:
750 mg/kg diet
No. of animals per sex per dose:
10 females per dose level for satellite group
Control animals:
yes, concurrent no treatment
Details on study design:
The test substance was administered at constant concentrations in the diet for 13 consecutive weeks. The test substance was administered via the diet two weeks premating, during gestation and up to euthanasia at or shortly after postnatal day 4.
Maternal examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Clinical signs and mortality were observed at least once daily (in the morning) and on working days also once in the afternoon.

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: Once during the acclimatisation period, once at initiation of the study prior to introduction of feed. The females of the satellite groups were weighed 4 days before gestation, on gestation days 0, 7, 14 and 21 and on postnatal days 1 and 4. Furthermore, all animals were weighed on the day of necropsy in order to determine their correct organ to body weight ratios.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Measured per cage over weekly periods by weighing the feeders (in g/animal/day).

WATER CONSUMPTION: No

GROSS NECROPSY: Yes
Organs weighed included ovaries, uterus (after counting of the implantation sites), thymus and all gross lesions.

HISTOPATHOLOGY / ORGAN WEIGHTS: Yes
Microscopic examination of the ovaries, uterus and thymus of the control and 750 mg/kg groups was performed. Examination was extended to the thymus of the females of the 30 and 150 mg/kg groups because of the effects observed in the 750 mg/kg group for this tissue/organ. Furthermore, the reproductive organs of females of the 30 and 150 mg/kg groups that were non-mated or non-pregnant were microscopically examined.
Ovaries and uterine content:
The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of implantations: Yes
Fetal examinations:
At the end of the gestation period, females were examined twice daily for signs of parturition. The litters were examined only daily for dead pups. The total litter size and numbers of each sex as well as the number of stillbirths, live and dead pups and grossly malformed pups were evaluated on days 1 and 4 of lactation. Mean pup weights were calculated as litter weight/number pups. The number of runts (< 2 sd from the litter mean) were noted and reported as well.

SACRIFICE
Pups were killed by hypothermia at < -18 °C.

GROSS NECROPSY
A necropsy was performed on stillborn pups and pups dying during the study; pups were examined externally for gross abnormalities and macroscopic abnormalities were recorded.
Statistics:
- Test substance analysis: Homogeneity: one way analysis of variance (Anova) using the sample location (1-5) as grouping factor. The test substance was considered to be homogeneously distributed in the diets if p > 0.01 and/or if the relative standard deviation (RSD) between the sample means was less than or equal to 15 %. Stability: one way analysis of variance (Anova) using time as grouping factor. The test substance was considered to be stable in the diets if p > 0.01 and/or if the mean concentration on the last day was between 80 and 120 % of the mean concentration on the first day (t =0). Achieved concentration: for each concentration level, the mean of the concentrations, as measured in the diet samples used for the assessment of the homogeneity, was considered to represent the achieved concentration. The content of the test substance in the diet was considered to be 'close to intended' if the mean measured concentration was between 80 and 120 % of the intended concentration.
- Body weight: one way analysis of covariance (covariate: body weight on day 0) followed by Dunnett's multiple comparison tests.
- Food consumption and food efficiency: one way analysis of variance (Anova) followed by L.S.D. tests.
- Fisher's exact probability test was used to evaluate the number of mated and pregnant females and females with live pups. Numbers of implantation sites and live and dead pups were evaluated by Kruskal-Wallis non-parametric analysis of variance followed by the Mann-Whitney U-test.
- The litter was used as the statistical unit for calculation of foetal values.
- Histopathological changes: Fisher's exact probability test. All tests were two-sided. Probability values of p<0.05 were considered significant.
Indices:
With regard to fertility and reproductive performance, the following parameters were calculated:
-Pre-coital time = time between the start of mating and successful copulation
- Duration of gestation = time between gestation day 0 and day of delivery
- Mating index = (number of females mated/number of females placed with males) x 100
- Male fertility index = (number of males that became sires/number of males placed with females) x 100
- Female fertility index = (number of pregnant females/number of females placed with males) x 100
- Female fecundity index = (number of pregnant females/number of females mated) x 100
- Gestation index = (number of females with live pups/number of females pregnant) x 100
- Number of lost implantations = number of implantations sites - number of pups born alive
- Post-implantation loss = [(number of implantation sites - number of pups born alive)/number of implantation sites] x 100
- Live birth index = (number of pups born alive/number of pups born) x 100
- Pup mortality day n = (number of dead pups on day n/total number of pups on day n) x 100
- Viability index day 1-4 = (number of pups surviving 4 days/total number of live pups on day 1) x 100
- Sex ratio day n = (number of male pups on day n/ total number of pups) x 100
Clinical signs:
not specified
Mortality:
mortality observed, treatment-related
Description (incidence):
One animal of the 750 mg/kg group was found dead on GD 22 (i.e. 37 days after the start of exposure).
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
An increased body weight change from GD 7-14 of the females of the 30 mg/kg group was noted, which was considered a chance finding. Mean body weights (change) of the females were similar among the control, 30 and 150 mg/kg group during the entire study. Mean body weight (changes) between PN 1-4 of the 750 mg/kg group was decreased; however, no statistical significance was reached for these findings.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
Food consumption of the female animals of the 750 mg/kg group was decreased (not statistically significantly) during the lactation period. During the premating and gestation periods food consumption of the females was similar in the control, 30, 150 and 750 mg/kg groups.

The test substance intake of the female animals of the 30, 150 and 750 mg/kg dose groups was respectively:
- Premating period days 0-7: 1.8, 9.0 and 44.5 mg/kg bw/day
- Premating period days 7-14: 1.8, 8.8 and 43.9 mg/kg bw/day
- Gestation period GD 0-7: 1.9, 9.6 and 44.5 mg/kg bw/day
- Gestation period GD 7-14: 2.0, 9.6 and 45.8 mg/kg bw/day
- Gestation period GD 14-21: 1.2, 6.2 and 35.9 mg/kg bw/day
- Lactation period PN 1-4: 1.7, 11.7 and 26.5 mg/kg bw/day
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not specified
Haematological findings:
not specified
Clinical biochemistry findings:
not specified
Urinalysis findings:
not specified
Behaviour (functional findings):
not specified
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Description (incidence and severity):
Mean absolute and relative uterus, ovary and thymus weights were similar in all groups.
Gross pathological findings:
effects observed, non-treatment-related
Description (incidence and severity):
No treatment related changes were observed. The animal found dead on day 37 was necropsied. Findings included yellow patches on the liver, yellow appearance of the small intestines, haemorrhagic discharge from the vagina and a haemothorax. The haemothorax was considered to be the probable cause of death. Most probably the haemothorax was caused by severe dystocia, since at necropsy the uterus contained 12 dead foetuses.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
no effects observed
Description (incidence and severity):
No treatment related histopathological changes were observed in the uterus, ovary and thymus of the female animals of the control and 750 mg/kg groups.
Histopathological findings: neoplastic:
not examined
Number of abortions:
not specified
Pre- and post-implantation loss:
effects observed, treatment-related
Description (incidence and severity):
- Mean number of implantations: 11.2 (control group), 10.8 (30 mg/kg), 11.6 (150 mg/kg), 10.5 (750 mg/kg).
- Post implantation losses [total implantation sites minus total live births at the first observation]: 13 (18.6 %), 16 (15.3 %), 5 (4.7 %) and 36 (42.9 %) for the control, 30, 150 and 750 mg/kg groups, respectively.
Total litter losses by resorption:
not specified
Early or late resorptions:
not specified
Dead fetuses:
no effects observed
Description (incidence and severity):
- Live birth index: 98, 97, 100 and 96 % in the control, 30, 150 and 750 mg/kg groups, respectively.
- Number of pups born (number of litters): 90 (8), 86 (8), 99 (9) and 50 (7) for the control, 30, 150 and 750 mg/kg groups, respectively.
- Number of stillborn pups (number of litters): 2 (1), 3 (2), 0 and 2 (2) for the control, 30, 150 and 750 mg/kg groups, respectively.
Changes in pregnancy duration:
no effects observed
Description (incidence and severity):
- Gestation index: 89, 100, 100 and 88 % in the control, 30, 150 and 750 mg/kg groups, respectively.
- Duration of Pregnancy: 21 -23 days
Changes in number of pregnant:
no effects observed
Description (incidence and severity):
- Pre-coital time: comparable among the control and the treated groups.
- Mating index: 90 -100 %
- Number of pregnant females per dose level: 9, 8, 9 and 8 for the control, 30, 150 and 750 mg/kg groups, respectively.
- Female fecundity index: comparable among the control and the treated groups.
- Female fertility index: comparable among the control and the treated groups.
Other effects:
effects observed, treatment-related
Description (incidence and severity):
Interpretation of the pre- and post-implantation loss data was complicated by the incidence of missing pups across groups. A variable incidence of pups "missing" after birth was recorded. The incidence of missing pups was statistically significantly higher than controls in the high-dose group, statistically significantly lower than controls in the mid-dose group, and not statistically different than controls in the low-dose group. The missing pups were presumed to have been cannibalised by the dams, but it is not known if the missing pups were alive or dead. It is also not known if some pups were cannibalised prior to being counted for litter size. This could account for the slightly lower number of recorded live births and the slightly higher post-implantation loss in the high-dose versus controls. The reason for missing pups cannot be determined on the basis of the data within the study. Missing pups could be due solely to a toxic behavioural effect on dams which caused a lack of, or abnormal, nurturing. It is clear that no malformations were noted at any observation point for any of the missing pups and no overt behavioural effects were noted; however some other effect could have caused the dam to eat them.
Key result
Dose descriptor:
NOAEL
Remarks:
fertility and developmental effects
Effect level:
150 mg/kg diet
Based on:
test mat.
Basis for effect level:
pre and post implantation loss
other: decreased number of pups delivered and increased pup mortality
Key result
Dose descriptor:
NOAEL
Effect level:
150 mg/kg diet
Based on:
test mat.
Basis for effect level:
body weight and weight gain
food consumption and compound intake
other: 150 mg/kg diet (equivalent to 6.2 - 11.7 mg/kg bw/day in females) was considered to be the NOAEL for maternal toxicity.
Key result
Abnormalities:
no effects observed
Reduction in number of live offspring:
effects observed, treatment-related
Description (incidence and severity):
- Pup mortality: 2.2, 3.5, 0 and 4 % for the control, 30, 150 and 750 mg/kg groups, respectively (PN 1); 16, 25, 3 and 65 % for the control, 30, 150 and 750 mg/kg groups, respectively (PN 4).
- Number viable: The viability index (PN 1-4) was 84, 75, 97 and 35 % in the control, 30, 150 and 750 mg/kg groups, respectively.
- Number live pups per litter: 11.0, 10.4, 11.0 and 6.9 for the control, 30, 150 and 750 mg/kg groups, respectively (PN 1); 10.6, 7.8, 10.7 and 4.2 for the control, 30, 150 and 750 mg/kg groups, respectively (PN 4).
- Number of stillborn pups (number of litters): 2 (1), 3 (2), 0 and 2 (2) for the control, 30, 150 and 750 mg/kg groups, respectively.
Changes in sex ratio:
no effects observed
Description (incidence and severity):
No difference was observed in the sex ratio between the groups.
Changes in litter size and weights:
effects observed, treatment-related
Description (incidence and severity):
- Litter weight: The mean pup weights and pup weight changes were similar in the treated groups when compared to the control group.
- Litter size: The mean number of pups delivered per litter amounted to 11.2, 10.8, 11.0 and 7.1 for the control, 30, 150 and 750 mg/kg groups, respectively.
Changes in postnatal survival:
effects observed, treatment-related
Description (incidence and severity):
There was an incidence of missing pups across groups. A variable incidence of pups "missing" after birth was recorded. The incidence of missing pups was statistically significantly higher than controls in the high-dose group, statistically significantly lower than controls in the mid-dose group, and not statistically different than controls in the low-dose group. The missing pups were presumed to have been cannibalised by the dams, but it is not known if the missing pups were alive or dead. It is also not known if some pups were cannibalised prior to being counted for litter size. This could account for the slightly lower number of recorded live births and the slightly higher post-implantation loss in the high-dose versus controls. The reason for missing pups cannot be determined on the basis of the data within the study. Missing pups could be due solely to a toxic behavioural effect on dams which caused a lack of, or abnormal, nurturing. It is clear that no malformations were noted at any observation point for any of the missing pups and no overt behavioural effects were noted; however some other effect could have caused the dam to eat them.
External malformations:
no effects observed
Description (incidence and severity):
- Grossly visible abnormalities: In the 30 mg/kg group, the number of cold pups was statistically significantly increased on PN 1 and 4. In addition on PN 4, the number of runts, pale pups and pups with no milk in the stomach was statistically significantly increased in the 30 mg/kg group. In the 150 mg/kg group the number of pale pups on PN 4 was statistically significantly increased. In the 750 mg/kg group the number of cold pups was statistically significantly increased on PN 1. As most effects were observed in the 30 mg/kg group only, these effects were not considered to be treatment related. Macroscopic observation of the stillborn pups revealed no abnormalities of the pups.
Key result
Dose descriptor:
NOAEL
Remarks:
postnatal toxicity
Effect level:
150 mg/kg diet
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: Based on the incidences of missing pups in the 750 mg/kg group, 150 mg/kg can be considered as a NOAEL for postnatal toxicity.
Key result
Abnormalities:
no effects observed
Key result
Developmental effects observed:
no
Conclusions:
The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.
Executive summary:

The toxicity of trichloromethylstannane [CAS # 993-16-8] in Wistar rats was examined using continuous administration via the diet for 13 consecutive weeks (OECD Test Guideline 408). In satellite groups of female rats a reproduction/developmental screening test (OECD Test Guideline 421) was performed to provide initial data on possible reproductive and developmental effects of trichloromethylstannane. The main study used four groups of 10 rats/sex (13 -week study) and the satellite study used four groups of 10 female rats (reproduction/developmental screening study). For both studies the control group was kept on control diet and three test groups received experimental diets containing 30, 150 and 750 mg/kg [ppm] of the test substance. The dose levels used in both studies were based on the results of a preceding dose range finding study.

In the satellite study female rats were fed their respective test diets beginning 2 weeks prior to the mating period, and continued on test diets through mating, gestation, and up to PN 4 or shortly thereafter. Male rats from the main study were mated after a premating period of 10 weeks with female rats of the satellite groups which were fed the same dose of test diets.

Clinical observations, growth, food consumption, food conversion efficiency, neurobehavioural testing, ophthalmoscopy, haematology, clinical chemistry, renal concentration test, urinalysis, organ weights and gross examination at necropsy, microscopic examination of various organs and tissues and assessment of various reproductive and developmental parameters were used as criteria for detecting the effects of treatment. 

The calculated doses during the pre-mating, gestation and lactation periods for the females receiving 30, 150, or 750 mg/kg trichloromethylstannane in the diet ranged from 1.2-2.0, 6.2-11.7 and 26.5-45.8 mg/kg body weight, respectively.

During the study one animal of the 750 mg/kg group was found dead on GD22. Most probably haemothorax caused by dystocia was the cause of death. No other mortalities or treatment-related clinical signs were observed in the female animals of the satellite groups.

Mean body weight, body weight change and food consumption was similar in the control and the 30 and 150 mg/kg groups. Mean body weight on PN 4 and mean body weight change PN 1-4 of the 750 mg/kg group was decreased, although not statistically significantly.

During the premating and gestation periods, mean food consumption of the female animals was similar in the control, 30 and 150 mg/kg groups. During the lactation period food consumption of the 750 mg/kg group was decreased (not statistically significantly).

No treatment-related effects on reproduction and development of the pups were observed in the 30 and 150 mg/kg groups.

In the 750 mg/kg group, a number of changes were seen indicative of a reproductive and developmental effect. One animal was found dead on GD22 (death was most probably caused by haemothorax caused by dystocia), post-implantation loss was 43 %, the number of pups delivered was 7.1 versus 11.2 in the control group, 3 females lost all pups between PN 1-4, and pup mortality between PN 1-4 in the 750 mg/kg group was 65 versus 16 % in the control group.

No treatment-related effects on pup weight and pup abnormalities were observed.

Absolute and relative organ weights (uterus, ovary and thymus) were similar among the groups. At microscopic examination of these organs no treatment-related histopathological changes were observed.

Based on reproductive and developmental effects (decreased number of pups delivered and increased post implantation loss and pup mortality) observed after mating of female animals of the 750 mg/kg satellite group with male animals of the main study, the mid-dose level 150 mg Trichloromethylstannane/kg diet (equivalent to 9.8 mg/ kg body weight/day in males and 6.2-11.7 mg/kg body weight for females) can be considered as a NOAEL for fertility and developmental effects.

Based on the effects on body weight and food consumption in the 750 mg/kg group, 150 mg Trichloromethylstannanel kg diet (equivalent to 6.2-11.7 mg/kg body weight/day) can be considered as a NOAEL for maternal toxicity.

The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.

Endpoint:
developmental toxicity
Type of information:
other: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
Study conducted on read across material
Justification for type of information:
Read-across test result from source substance MMTC to target substance MMT(EHTG).
This data requirement is fulfilled by read-across. Justification for the read-across of this test result is provided in Section 7.1 Toxicokinetics. The simulated gastric hydrolysis study shows rapid and complete conversion of MMT(EHTG) to MMTC. Based on this result MMTC fulfils the requirements of being a source compound for studies required for MMT(EHTG) where the endpoint is based on oral exposure. The study on MMTC can be applied both quantitatively and qualitatively for the end point for MMT(EHTG).
Reason / purpose:
read-across: supporting information
Reason / purpose:
other: This study attempted to replicate the earlier study and expand upon it
Qualifier:
equivalent or similar to
Guideline:
other: EPA OPPTS 870.6300 (Developmental Neurotoxicity)
Version / remarks:
The second study was designed to be more consistent with the dosing paradigm of standard developmental neurotoxicity studies
Qualifier:
equivalent or similar to
Guideline:
other: OECD 426
Principles of method if other than guideline:
Concern for neurotoxicity produced by organotin exposure during development has been raised by published findings of a deficit on a runway learning task in rat pups peri-natally exposed to MMT (Noland EA, Taylor DH, Bull RJ. Monomethyl and trimethyltin compounds induce learning deficiencies in young rats. Neurobehav. Toxicol. Teratol. 1982; 4: 539 to 44).. The objective of these studies was to replicate the earlier publication and further define the dose-response characteristics of MMT following perinatal exposure.
In Experiment 1, female Sprague–Dawley rats were exposed via drinking water to MMT (0, 10, 50, 245 ppm) before mating and throughout gestation and lactation (until weaning at postnatal day [PND] 21). Behavioural assessments of the offspring included a runway test (PND 11) in which the rat pups learned to negotiate a runway for dry suckling reward, motor activity habituation (PNDs 13, 17, and 21) and learning in the Morris water maze (as adults). Other endpoints in the offspring included measures of apoptosis (DNA fragmentation) at PND 22 and as adults, as well as brain weights and neuropathological evaluation at PND 2, 12, 22, and as adults.
In Experiment 2, pregnant rats were exposed from gestational day 6 until weaning to 500 ppm MMT in drinking water. The offspring behavioural assessments again included the runway task (PND 11), motor activity habituation (PND 17) and Morris water maze (as adults).
GLP compliance:
not specified
Limit test:
no
Specific details on test material used for the study:
- Source: Aldrich, Milwaukee, WI, USA
Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River, Raleigh, North Carolina, USA
- Strain: Sprague-Dawley (CD)
- Age at study initiation: 53 to 54 days old
- Females (if applicable) nulliparous and non-pregnant: Yes for Experiment 1; for Experiment 2, timed-pregnant rats were received at gestational day (GD) 2
- Housing: Individually in AAALAC-International accredited rooms on Beta-Chip bedding; prior to breeding in Experiment 1, females were housed in pairs. On PND 21, the offspring were weaned and the littermates separated and housed individually.
- Diet: ad libitum; Purina Rodent Chow 5001 prior to breeding and for weaned offspring and Purina Rodent Chow 5008 following breeding.
- Water: ad libitum through polypropylene/polyethylene water bottles containing double ball-bearing sipper tubes
- Acclimation period: Yes; time period not reported

ENVIRONMENTAL CONDITIONS
- Temperature: 19-21 °C
- Humidity: 40-60 %
- Air changes (per hr): not reported
- Photoperiod: Experiment 1: reverse 12 hour light / 12 hour dark cycle - lights on at 12:00 h; Experiment 2: lights on at 06:00 h
Route of administration:
oral: drinking water
Vehicle:
water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: dissolved in distilled/deionised water

DIET PREPARATION not applicable

VEHICLE
- Concentration in vehicle: 10, 50 and 245 ppm (5, 25 and 120 mg Sn/L) for Experiment 1; 500 ppm (245 mg Sn/L) in Experiment 2
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Analyses were conducted to verify the concentration and speciation of the methyltins in the MMT solutions over days in the water bottles. It was of interest to determine if, and to what extent, interconversions in methyltin speciation occurred under conditions of the study.
The stock solution and solutions of the low and high test concentrations were sampled daily for 5 days in water bottles under conditions of the animal exposure. Analysis of MMT, DMT, and trimethyl tin (TMT) were determined using ion chromatography (IC) with inductively coupled plasma mass spectrometer (ICP-MS). In addition, total tin levels were measured using inductively coupled plasma optical emission spectrometer (ICP-OES).
Quality control checks were performed after each five to six runs; recoveries of 80 to 120 % were considered acceptable. For MMT, the limit of detection (LOD) was 10 ng Sn/mL, and for DMT and TMT, LOD was 1 ng Sn/mL.

The results of these analyses indicated that, as prepared, the high concentration was about 5 % higher than the nominal concentration of 120 mg Sn/L, and the low concentration was indeed 5 mg Sn/L. The low concentration showed 4 % decrease from days 4 to 5, but the high concentration did not change appreciably. Since bottles were changed every 3 to 4 days, it was concluded there was no significant loss of Sn under conditions of use. Furthermore, there was no detectable DMT or TMT in the MMT water samples at any time, indicating that if any changes in speciation occurred, it would represent only a negligible fraction of the nominal concentration.
Details on mating procedure:
EXPERIMENT 1
- Impregnation procedure: Cohoused
- M/F ratio per cage: 1/2. Two receptive females (i.e. late stage pro-oestrus) were placed with a breeder male
- Length of cohabitation: Late in the afternoon and removed the next day at lights on

EXPERIMENT 2
- Impregnation procedure: Purchased timed pregnant
- Proof of pregnancy: Sperm positive considered gestational day 0
Duration of treatment / exposure:
Experiment 1: 2 weeks prior to breeding and through gestation and lactation until PND 21
Experiment 2: Gestation day 6 through gestation and lactation
Frequency of treatment:
continuous in drinking water
Dose / conc.:
10 ppm (nominal)
Remarks:
Experiment 1
Dose / conc.:
50 ppm (nominal)
Remarks:
Experiment 1
Dose / conc.:
245 ppm (nominal)
Remarks:
Experiment 1
Dose / conc.:
500 ppm
Remarks:
Experiment 2
No. of animals per sex per dose:
Experiment 1: 30 females
Experiment 2: 18 females
Control animals:
yes, concurrent no treatment
Details on study design:
- Dose selection rationale: The objective of these studies was to replicate the earlier publication and further define the dose-response characteristics of MMT following perinatal exposure.
- Rationale for animal assignment (if not random): Experiment 1: randomly housed in pairs upon arrival then rearranged and paired according to synchronised oestrous cycles.
Maternal examinations:
BODY WEIGHT: Yes
- Time schedule for examinations: Rats were weighed twice weekly

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: Water bottles were changed and weighed twice weekly
Ovaries and uterine content:
The ovaries and uterine content was examined after termination: Yes. Non-pregnant females were euthanised and examined for foetal resorption.
Fetal examinations:
EXPERIMENT 1
When possible, the litters were culled to eight males on postnatal day (PND) 1 (day of birth = PND 0). In a few cases, female pups were used to maintain equal litter sizes. Only male offspring (one from each litter) were tested in the neurobehavioral tasks. Offspring were weighed at least weekly throughout the study.

EXPERIMENT 2
When possible, litters (n = 17 control, n = 14 MMT) were culled to four males and four females on PND 4. Both male and female offspring (one from each litter) were tested in neurobehavioral tasks with the exception of the runway task, in which only males were tested.

NEUROBEHAVIORAL ASSESSMENTS
RUNWAY LEARNING TEST
The runway was a Plexiglas testing apparatus consisting of an alley (38 cm long, 7.5 cm wide, 10 cm high) and a goal box (17 x 26 x 10 cm). Both the testing apparatus and the inter-trial interval holding cage were maintained at 37 °C through the use of water-circulating heating pads. The task was an appetitive learning paradigm in which a food-deprived PND 11 rat pup was trained to negotiate a runway for a dry suckling reward from its anaesthetised dam in the goal box. Training consisted of alternating reinforced (R) and non-reinforced (N) trials. The pup was placed at the end of the runway facing away from the dam and the time to reach the goal box was recorded. On (R) trials, the pup was given 15 s of dry suckling before being transferred to the holding cage. On (N) trials, the pup was promptly placed in the holding cage upon reaching the end of the runway. If the pup failed to find the dam within the allotted time, the experimenter guided it down the runway for either reinforcement or to be immediately placed in the holding cage. Extinction immediately followed acquisition. The specific parameters for each experiment are outlined below.

- Experiment 1
Dams were anaesthetised using a drug cocktail (42.5 mg chloral hydrate, 8.86 mg pentobarbital and 21.2 mg magnesium sulfate, in each mL of sterile aqueous solution containing water, 33.8 % propylene glycol and 14.25 % ethyl alcohol). The dams were dosed with 2 mL/kg body weight i.p. approximately 15 min before testing began. When fully anaesthetised, the dam was placed in the goal box at the end of the runway to serve as the reinforcer for the pup.
Pups (n = 10/treatment group, except n = 11 at 245 ppm) were food-deprived for 10 h prior to testing and tested on PND 11 during their dark cycle. Acquisition consisted of 25 trials with (R) and (N) trials alternating on every other trial and the maximum time was set at 120 s. Between each trial, the pup was placed in the holding cage for 15 s. Extinction began on the 26th trial. During this time, the pup was removed to the holding cage without gaining access to the dam on every trial. The maximum time was set at 100 s. Criterion to extinction was two consecutive trials with latencies of 100 s. After this criterion was reached, the pup was no longer tested; however, all pups were tested until they met criterion, regardless of the number of trials required.

- Experiment 2
Dams were anaesthetised using Nembutal sodium solution (50 mg/mL). The dams were dosed with 2 to 2.2 mL/kg body weight i.p. As before, testing began when the dam was fully anaesthetised.
In this paradigm, pups (n = 17 control, n = 14 MMT) were food-deprived for 8 h prior to testing and tested on PND 11 during their light cycle (pilot studies had indicated that 8 h deprivation was not different from 10 h in terms of motivation and task performance.) Testing began with a preliminary training session of five initial training (R) trials, followed by a 2 min retention interval in the holding cage. There were then 25 acquisition trials in which (R) and (N) trials alternated in blocks of five trials, beginning and ending with 5(R) trials. The inter-trial interval was 8 s. During acquisition, the pup was permitted 100 s before the trial ended and, if unsuccessful, it was guided to the dam. Extinction began on the 26th trial. Criterion to extinction was one trial with a latency of 100 s and a maximum of 10 extinction trials were run.

MOTOR ACTIVITY
Motor activity data were collected using an automated figure-eight chamber. Activity was measured as interruptions (counts) of any of the eight photocell beams distributed around the maze. Counts were recorded over 5 min intervals for a 30 min testing session.
- In Experiment 1, motor activity was assessed in males at PNDs 13, 17 and 21 (n = 10 control, n = 9 at 50 ppm, n = 11 at 10 ppm and n = 10 at 245 ppm).
- In Experiment 2, only PND 17 male and female offspring (one male and one female from each litter; n = 17 control, n = 14 MMT) were tested.

MORRIS WATER MAZE
Spatial learning and memory was evaluated in adults (starting at about 70 days of age) using a Morris water maze which consisted of a round galvanised steel tank 140 cm in diameter and filled with tap water (24–27 °C) to a depth of approximately 44 cm. A round, Plexiglas escape platform (9 cm in diameter) was positioned 2 cm beneath the surface of the water. The water was rendered opaque using black Tempra paint and was changed daily. The trials were videotaped and the image digitised for computer analysis using maze-tracking software (HVS Image, Ormond Cresent, Hampton, UK). Dependent variables included swim speed, latency and path length to find the platform and time spent in the outer edge of the tank. The tank was digitally divided into three concentric zones (annuli) of equal width, and time spent in each zone was also analysed.
For the spatial training, the platform was placed in a fixed quadrant. Acquisition occurred during two trials each day over a total period of 9 days (5 days training, 2 days off, 4 days training). The rat was placed in the water at one of four starting points which varied such that the rat never started in the same place within 2 days. The trials continued until the rat mounted the platform, or for a maximum of 60 s. If the rat did not find the platform within the 60 s, it was guided there by the observer.
After 15 s on the platform, the rat was placed in a holding cage for 5 min before the second trial began. On the 10th day, a probe trial was conducted in which the platform was removed and the rat’s tendency to search in the correct quadrant (where the platform had been) was measured over 60 s. The Gallagher proximity score, a measure of cumulative distance from the platform and percent total path length within each quadrant, were used to assess quadrant bias.
Following the memory probe trial, a visible target task (cued trial) was conducted using a raised platform of a contrasting colour to confirm that the tested animals were not visually impaired.
In Experiment 1, only males were tested in the water maze (n = 9 control, n = 10 at 10 ppm, n = 8 at 50 ppm, and n = 7 at 245 ppm) whereas both males and females were tested in Experiment 2 (n = 16 control, n = 14 MMT 500 ppm).

NEUROPATHOLOGY (EXPERIMENT 1 ONLY)
For neuropathological evaluations, male rats (n = 6–7/dose at PND 1, n = 7–9/dose at PND 12, n = 7–11/dose at PND 22, and n = 7–10/dose at adult age, about 85 to 90-days old) were deeply anaesthetised with pentobarbital and perfused via the left ventricle with buffered 4 % formaldehyde:0.1 % gluteraldehyde.
Sagittal blocks of tissue were embedded in paraffin and sectioned to include all major structural landmarks of the brain in each section (e.g., olfactory bulb, striatum, cerebral cortex, hippocampus, thalamus, hypothalamus, brainstem and cerebellum).
Twenty-four homologous sections of the brain from each rat, from each age, at each dose, were stained with haematoxylin and eosin.
Brains from all control and high-dose rats, at all ages, were evaluated by a qualified pathologist who was blind to the treatment. Step-down assessments, i.e., evaluation of the lower dose groups, were only conducted in the adult rats due to findings in the high-dose group; no abnormalities were observed at the younger ages. Any changes observed were subjectively scored in both number as well as nature of the change as follows: (1) minimal; (2) slight/mild; (3) moderate; (4) moderately severe; (5) severe.

NEUROCHEMICAL ASSESSMENT AND BRAIN WEIGHT (EXPERIMENT 1 ONLY)
Male rats were decapitated under CO2-induced anaesthesia on PND 1 (at culling), PND 22, and adult (80 to 90-days old). At culling, all pups within a litter were combined, and at older ages all rats came from different litters. Brains were removed from the calvaria, free of meninges, and weighed. The PND 22 and adult brains were dissected free-hand into the following regions: brainstem, neocortex, hippocampus and cerebellum. Each region was immediately frozen in 2-methyl butane on dry ice for 30 s, weighed and stored at -80 °C. Brain tissues were collected from Experiment 1 only (n = 4–9/dose/region).
DNA fragmentation was used as an indicator of apoptotic cell death and was quantified using a Cell Death ELISA procedure. The kit has been adapted for use with intact tissue and validated with both fresh and frozen brain tissue, and the results have been corroborated qualitatively by agarose gel and TUNEL data. In short, the enzyme-linked immunosorbent assay (ELISA) uses antibodies to bind fragmented DNA characteristic of apoptotic cell death. The bound fragments (i.e., nucleosomes) are then quantified photometrically.
Statistics:
Continuous data (e.g. body weight, water intake, activity counts, etc.) were analysed using a general linear model ANOVA (SAS, Cary, North Carolina, USA). Extinction in the runway test was analysed with a survival model for censored data (SAS), and count data (e.g. number of pups learning, pregnancy rate) were compared using Fisher's exact test (SAS). When the same rat was used in repeated tests (e.g. repeated motor activity testing, body weights over time), the analyses included time as a repeated factor. For apoptosis data, all brain region values were compared to their respective controls and arcsine transformed prior statistical analyses. Following a significant overall analysis, Dunnett's t-test was used to compare dose groups with the control. In all cases resulting probability values <0.05 were considered significant.
Clinical signs:
not specified
Mortality:
not specified
Body weight and weight changes:
no effects observed
Description (incidence and severity):
EXPERIMENT 1
There were no treatment-related differences in body weight throughout exposure.

EXPERIMENT 2
Body weight was not different in the treated group.
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
effects observed, treatment-related
Description (incidence and severity):
EXPERIMENT 1
Fluid intake increased somewhat during gestation (about 30 to 40 %) and was much higher (more than double) during lactation. There were, however, no differences in fluid intake across treatment groups at any time during the study. MMT intake was much greater during lactation.

EXPERIMENT 2
There was a significant depression of fluid intake across almost all days of treatment with MMT 500 ppm. A significant day-by-intake interaction was followed with step-down analyses, which indicated that only the intake measured 3 days post-parturition was not different. During gestation, MMT consumption was about 80 to 88 % of control levels, and during lactation, 82 to 88 % of control. As in Experiment 1, the intake during lactation nearly doubled.
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not examined
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
not examined
Histopathological findings: neoplastic:
not examined
Number of abortions:
not specified
Pre- and post-implantation loss:
not examined
Description (incidence and severity):
EXPERIMENT 2
Two rats in the MMT group did not deliver. These rats were not evaluated for implantation sites.
Total litter losses by resorption:
no effects observed
Description (incidence and severity):
EXPERIMENT 1
Necropsy of all non-pregnant rats revealed resorptions in only two control rats and one rat from the low-dose group. Incidence of resorptions was not statistically different across treatment groups.
Early or late resorptions:
not examined
Dead fetuses:
not examined
Changes in pregnancy duration:
effects observed, non-treatment-related
Description (incidence and severity):
EXPERIMENT 1
The authors typically find that most of the Sprague-Dawley rats deliver within a 24 h period which is specified as PND 0. In the present study, however, 11 of the 44 (25 %) rats delivered later than that time window. Incidence of late delivery was not statistically different across treatment groups.

EXPERIMENT 2
All of the deliveries occurred when expected.
Changes in number of pregnant:
no effects observed
Description (incidence and severity):
EXPERIMENT 1
Despite the timed breeding, pregnancy rate was very low with only 44 of 120 (37 %) rats delivering litters (10, 11, 11, and 12 litters for control, 10, 50 and 245 ppm, respectively). Incidence of pregnancy was not statistically different across treatment groups.

EXPERIMENT 2
All of the timed-pregnant females in the control group delivered, but two in the MMT group did not.
Other effects:
effects observed, non-treatment-related
Description (incidence and severity):
EXPERIMENT 2
In the MMT group, one litter consisted of all females and was not used, and another litter was killed by the dam shortly after birth.
Key result
Dose descriptor:
NOAEL
Remarks:
Experiment 1
Effect level:
245 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: There were no effects on the dams reported
Key result
Dose descriptor:
NOAEL
Remarks:
Experiment 2
Effect level:
500 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: There were no effects on the dams reported
Key result
Abnormalities:
no effects observed
Fetal body weight changes:
not examined
Description (incidence and severity):
EXPERIMENT 1
Body weights across time were similar across treatment groups throughout the entire study. In addition, there were no differences in weights of the pups selected for each behavioural test.

EXPERIMENT 2
Body weight changes during the lactation period showed a significant dose-by-sex interaction, but step-down analyses showed that on 1 day only (PND 11), male and female pups in the control group were different by about 4 g; this was considered to be within biological variability. There were no treatment effects on body weight after weaning.
Reduction in number of live offspring:
no effects observed
Changes in sex ratio:
no effects observed
Description (incidence and severity):
EXPERIMENT 1
There were no treatment-related differences in the number of males and females per litter.

EXPERIMENT 2
There were no differences in the sex ratio within the litters.
Changes in litter size and weights:
no effects observed
Description (incidence and severity):
EXPERIMENT 1
There were no significant differences in the number of pups per litter across treatment groups, as follows (mean number per litter ± S.E.): control, 12.5 ± 1.6; 10 ppm, 15.2 ± 0.6, 50 ppm, 13.1 ± 1.3, and 245 ppm, 13.4 ± 1.5.
Litter birth weights were similar across treatment groups.

EXPERIMENT 2
There were no differences in the number of pups per litter (control, 11.9 ± 0.4; MMT, 12.2 ± 0.8).
Changes in postnatal survival:
not specified
External malformations:
not examined
Skeletal malformations:
not examined
Visceral malformations:
not examined
Other effects:
effects observed, treatment-related
Description (incidence and severity):
RUNWAY TESTING
- Experiment 1
Almost all of the pups learned to traverse the runway to the goal box. Using a criterion of at least one latency (time to reach the goal box) less than the maximum time of 120 s, only one pup (high dose) did not learn the task. While highly variable, the latency data did not reveal a significant treatment-related difference.
The time to extinction was also quite variable, with one pup (low-dose) requiring 46 trials to meet the criterion of two consecutive latencies of 100 s. The median number of trials to reach criterion for each dose group was as follows: control, 17; 10 ppm, 15.5, 50 ppm, 20.5; 245 ppm, 20.5.

- Experiment 2
Fewer pups were able to learn the different paradigm used in the second study. One control and five treated pups did not meet the criterion of having at least one latency less than 100 s during acquisition; however, this difference did not attain statistical significance (Fisher’s exact p = 0.067). Furthermore, one pup in each group did not extinguish within the 10 trials.
A different pattern of responding was elicited by the procedure of batched reinforced (R) and non-reinforced (N) trials. In general, latencies became shorter during the R trials and longer during the N trials. This pattern indicates repeated acquisition and extinction, and was most evident in the last two sets of trials. Trend analyses were conducted on each set of trials to determine if the changes within each block were significant (either increasing or decreasing). For the control group, the last two blocks showed significant slopes in the latencies (mean ± S.E. slopes for the last N-trials, 8.7 ± 3.0; last R trials, -7.8 ± 3.3). On the other hand, the MMT group showed significant slopes during the third and fourth blocks (middle R trials, -12.0 ± 2.9; last N trials 11.0 ± 4.0), but not the fifth (last R trials, -6.0 ± 5.3, p = 0.074). Using ANOVA to evaluate group differences, only one trial showed a significant difference between the groups (fourth trial of the middle R-trials).
For the cumulative percentages of the groups reaching criterion (one trial with latency of 100 s) across each extinction trial, there were no significant differences. The median number of trials to reach criterion were: control, 4 trials; MMT, 5.5 trials.

MOTOR ACTIVITY
- Experiment 1
Total motor activity counts during 30-min sessions were lowest at PND 13 (means ranging from 20.3 to 31.2), and increased over PND 17 (means 46.5 to 72.7) and 21 (means 98.7 to 120.3). Analysis of the within-session activity (in 5 min intervals) showed no habituation during the session at PNDs 13 and 17. By PND 21, habituation was evident. There were no group differences on any of these measures.

-Experiment 2
Motor activity testing was only conducted on PND 17, at which time there were no differences between the control and MMT-treated groups (mean ± S.E. for each group: control, 99.6 ± 7.0 total counts; 500, 108.3 ± 8.5). Habituation was evident in both dose groups.

MORRIS WATER MAZE
- Experiment 1
All rats learned the location of the hidden platform over the two weeks of training, as evidenced by decreasing latency to find the platform with repeated training. Daily blocks and training trials showed significant changes over testing.
Latency, path length, swim speed and most spatial distribution variables were not different across treatment groups. The only significant finding was increased time in the middle zone in the 50 ppm group on day 6 only; this was not supported by other findings and is probably not biologically relevant.
During the memory probe, all rats spent the most time searching in the quadrant where the platform had been located. There were no differences in quadrant bias, Gallagher index or spatial distribution variables. For the visual function test, there were no differences in the latency to reach a raised, visible platform, as follows (mean ± S.E.): control, 27.4 ± 4.7 s; 10 ppm, 25.3 ± 2.6 s; 50 ppm, 31.4 ± 7.0 s; 245 ppm, 24.0 ± 4.4 s.

- Experiment 2
As in Experiment 1, all rats learned the spatial task, indicated by significant changes in daily blocks and individual training trials. There were, however, no interactions with treatment or sex on any endpoint. Likewise, there were no differences on any measures during the memory probe, or during the visual probe (visible platform).

BRAIN WEIGHT (EXPERIMENT 1 ONLY)
There was a marginal effect on brain weight, although the overall dose effect at p < 0.07 did not reach the criterion for statistical significance. There was no interaction of treatment and age, and collapsed across ages, the high dose group showed a 5 % decrease in weight.

NEUROPATHOLOGY (EXPERIMENT 1 ONLY)
No histological alterations were observed in the brains of MMT-treated offspring killed on PND 1, 12, or 22. There were, however, changes in the brains of the offspring evaluated as adults. The cerebral cortical lesion was characterised by 2 to 4 mm diameter, round vacuoles of varying size, in the grey matter neuropil, localised to the region of the orbital cortex.
Furthermore, the focal location of the lesion was very similar across animals, supporting the conclusion of a treatment-related effect. Myelin was not affected. Two of eight (25 %) adult high-dose offspring had vacuolation scored as ‘‘slight/mild’’ (‘2’), whereas one of seven (14 %) of the mid-dose group, and three of ten (30 %) low-dose rats had similar vacuolation scored as ‘‘minimal’’ (‘1’).
There were no such findings in control rats. Although there was no increase in incidence or more widespread localisation of this lesion with increasing dose, the change was scored as slightly greater severity in the high-dose offspring (‘2’s) than that of the lesions in the lower dose groups (‘1’s). There were no histopathological findings in any other major brain region other than this specific area of the cerebral cortex.
These adult rats had been tested previously in the Morris water maze. Review of the water maze data for the rats showing vacuolation revealed that their performance was not different from the unaffected rats. Thus, no within-individual correlations between vacuolation and behavioural performance could be made.

APOPTOSIS (EXPERIMENT 1 ONLY)
The data for PND 22 brainstem were not analysed due to insufficient sample size. Data from PND 22 and adult cortex show no treatment-related difference in DNA fragmentation. Similarly, the PND 22, and adult, neocortex and hippocampus remained unaffected by perinatal MMT exposure, as did the adult brainstem.
Key result
Dose descriptor:
NOAEL
Remarks:
Experiment 1
Effect level:
245 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: The author concluded that perinatal exposure to MMTC, even at concentrations which decreased maternal fluid intake, did not result in reproductive, neurobehavioral or cognitive deficits.
Key result
Dose descriptor:
NOAEL
Remarks:
Experiment 2
Effect level:
500 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: The author concluded that perinatal exposure to MMTC, even at concentrations which decreased maternal fluid intake, did not result in reproductive, neurobehavioral or cognitive deficits.
Key result
Abnormalities:
no effects observed
Key result
Developmental effects observed:
no

Table 1: Fluid intake (average and range of means, mL/day), body weight (average and range of means, g) and calculated MMT intake (mg/kg/day) for each concentration of MMT (ppm) throughout exposure

 

Concentration

Intake

Weight

MMT

Experiment 1

Pre-breeding

0

28.9 (27.0 - 30.4)

266.8 (253 - 271.1)

-

10

26.5 (24.5 - 27.7)

270.6 (254.9 - 274.6)

1.0

50

28.2 (27.1 - 29.1)

268.0 (255.5 - 271.6)

5.3

245

25.7 (23.6 - 26.8)

270 (256.0 - 274.3)

23.3

Gestation

0

39.9 (36.1 - 48.1)

330.8 (274.5 - 418.1)

-

10

36.1 (30.7 - 43.5)

330.6 (280.8 - 414.5)

1.1

50

43.4 (35.1 - 50.6)

336.3 (276.4 - 420.3)

6.5

245

36.5 (30.8 - 44.7)

336.7 (278.4 - 422.3)

25.7

Lactation

0

68.4 (48.2 - 92.9)

339.4 (336.2 - 346.3)

-

10

65.2 (44.7 - 86.8)

336.8 (322.6 - 348.3)

1.8

50

75.0 (51.4 - 95.9)

343.9 (332.3 - 356.6)

10.6

245

62.8 (47.8 - 82.1)

347.5 (335.8 - 352.3)

41.6

Experiment 2

Gestation

0

38.2 (33.1 - 44.0)

284.7 (231 - 346.9)

-

500

32.4 (28.5 - 37.4)

290.5 (233.9 - 356)

55.8

Lactation

0

71.7 (40.8 - 96.3)

314.7 (304.0 - 328.8)

-

500

60.8 (36.9 - 85.1)

322.5 (310.9 - 333.8)

94.3

 

Conclusions:
These results indicate that perinatal exposure to the test substance, even at concentrations which decrease maternal fluid intake, does not result in significant neurobehavioral or cognitive deficits.
Executive summary:

The objective of these studies was to replicate an earlier publication and further define the dose response characteristics of monomethylitn following perinatal exposure.

In Experiment 1, female Sprague-Dawley rats were exposed via drinking water to the test substance (0, 10, 50 and 245 ppm; equivalent to 0, 5, 25 and 120 mg Sn/L, respectively) before mating and throughout gestation and lactation (until weaning at postnatal day [PND] 21). Behavioural assessments of the offspring included a runway test (PND 11) in which the rat pups learned to negotiate a runway for dry suckling reward, motor activity habituation (PNDs 13, 17 and 21) and learning in the Morris water maze (as adults). Other endpoints in the offspring included measures of apoptosis (DNA fragmentation) at PND 22 and as adults, as well as brain weights and neuropathological evaluation at PND 2, 12, 22 and as adults.

In Experiment 2, pregnant rats were exposed from gestational day 6 until weaning to 500 ppm (245 mg Sn/L) in drinking water. The offspring behavioural assessments again included the runway task (PND 11), motor activity habituation (PND 17) and Morris water maze (as adults).

The results of Experiment 1 showed that there were no effects on any measure of growth, development, cognitive function or apoptosis following exposure to the test substance. There was a trend towards decreased brain weight in the high dose group. In addition, there was vacuolation of the neuropil in a focal area of the cerebral cortex of the adult offspring in all dose groups (1 -3 rats per treatment group).

In the second study, exposed females consumed significantly less water than the controls throughout both gestation and lactation, although neither dam nor pup weights were affected. As in Experiment 1, exposure did not alter pup runway performance, motor activity or cognitive function. These results indicate that perinatal exposure to the test substance, even at concentrations which decrease maternal fluid intake, does not result in significant neurobehavioral or cognitive deficits. While mild histological lesions were observed in the brain of adult offspring, the biological significance of this restricted finding in unclear.

Effect on developmental toxicity: via oral route
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
6.2 mg/kg bw/day
Study duration:
subacute
Species:
rat
Quality of whole database:
A screening study conducted in accordance with standardised guidelines under GLP conditions on a read across substance is available as is a paper containing two developmental neurotoxicity studies. The quality of the database is therefore considered to be adequate.
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

When assessing for reproductive effects of MMTC, there are two studies to consider: an OECD 421 screening study and a published study in which two developmental neurotoxicity studies were carried out.

The toxicity of trichloromethylstannane [CAS # 993-16-8] in Wistar rats was examined using continuous administration via the diet for 13 consecutive weeks (OECD Test Guideline 408). In satellite groups of female rats a reproduction/developmental screening test (OECD Test Guideline 421) was performed to provide initial data on possible reproductive and developmental effects of trichloromethylstannane. The main study used four groups of 10 rats/sex (13 -week study) and the satellite study used four groups of 10 female rats (reproduction/developmental screening study). For both studies the control group was kept on control diet and three test groups received experimental diets containing 30, 150 and 750 mg/kg [ppm] of the test substance. The dose levels used in both studies were based on the results of a preceding dose range finding study.

In the satellite study female rats were fed their respective test diets beginning 2 weeks prior to the mating period, and continued on test diets through mating, gestation, and up to PN 4 or shortly thereafter. Male rats from the main study were mated after a premating period of 10 weeks with female rats of the satellite groups which were fed the same dose of test diets.

Clinical observations, growth, food consumption, food conversion efficiency, neurobehavioural testing, ophthalmoscopy, haematology, clinical chemistry, renal concentration test, urinalysis, organ weights and gross examination at necropsy, microscopic examination of various organs and tissues and assessment of various reproductive and developmental parameters were used as criteria for detecting the effects of treatment. 

The calculated doses during the pre-mating, gestation and lactation periods for the females receiving 30, 150, or 750 mg/kg trichloromethylstannane in the diet ranged from 1.2-2.0, 6.2-11.7 and 26.5-45.8 mg/kg body weight, respectively.

During the study one animal of the 750 mg/kg group was found dead on GD22. Most probably haemothorax caused by dystocia was the cause of death. No other mortalities or treatment-related clinical signs were observed in the female animals of the satellite groups.

Mean body weight, body weight change and food consumption was similar in the control and the 30 and 150 mg/kg groups. Mean body weight on PN 4 and mean body weight change PN 1-4 of the 750 mg/kg group was decreased, although not statistically significantly.

During the premating and gestation periods, mean food consumption of the female animals was similar in the control, 30 and 150 mg/kg groups. During the lactation period food consumption of the 750 mg/kg group was decreased (not statistically significantly).

No treatment-related effects on reproduction and development of the pups were observed in the 30 and 150 mg/kg groups.

In the 750 mg/kg group, a number of changes were seen indicative of a reproductive and developmental effect. One animal was found dead on GD22 (death was most probably caused by haemothorax caused by dystocia), post-implantation loss was 43 %, the number of pups delivered was 7.1 versus 11.2 in the control group, 3 females lost all pups between PN 1-4, and pup mortality between PN 1-4 in the 750 mg/kg group was 65 versus 16 % in the control group.

No treatment-related effects on pup weight and pup abnormalities were observed.

Absolute and relative organ weights (uterus, ovary and thymus) were similar among the groups. At microscopic examination of these organs no treatment-related histopathological changes were observed.

Based on reproductive and developmental effects (decreased number of pups delivered and increased post implantation loss and pup mortality) observed after mating of female animals of the 750 mg/kg satellite group with male animals of the main study, the mid-dose level 150 mg Trichloromethylstannane/kg diet (equivalent to 9.8 mg/ kg body weight/day in males and 6.2-11.7 mg/kg body weight for females) can be considered as a NOAEL for fertility and developmental effects.

Based on the effects on body weight and food consumption in the 750 mg/kg group, 150 mg Trichloromethylstannanel kg diet (equivalent to 6.2-11.7 mg/kg body weight/day) can be considered as a NOAEL for maternal toxicity.

The NOAEL for general sub-chronic toxicity and maternal toxicity, fertility and developmental effects was placed at 150 mg trichloromethylstannane per kg diet.

The experimental design of the OECD Guideline 421 screening study is considered to be limited; all potential toxic effects are not assessed in every phase of the study. Therefore a weight-of-evidence analysis should preferentially consider more robust studies in evaluating potential hazards. The Developmental Neurotoxicity [DNT] study is a more robust study than the OECD 421. The DNT is outlined under US EPA Guideline 870.6300 and is equivalent to OECD Guideline 426. 

The objective of these studies was to replicate an earlier publication and further define the dose response characteristics of monomethylitn following perinatal exposure.

In Experiment 1, female Sprague-Dawley rats were exposed via drinking water to the test substance (0, 10, 50 and 245 ppm; equivalent to 0, 5, 25 and 120 mg Sn/L, respectively) before mating and throughout gestation and lactation (until weaning at postnatal day [PND] 21). Behavioural assessments of the offspring included a runway test (PND 11) in which the rat pups learned to negotiate a runway for dry suckling reward, motor activity habituation (PNDs 13, 17 and 21) and learning in the Morris water maze (as adults). Other endpoints in the offspring included measures of apoptosis (DNA fragmentation) at PND 22 and as adults, as well as brain weights and neuropathological evaluation at PND 2, 12, 22 and as adults.

In Experiment 2, pregnant rats were exposed from gestational day 6 until weaning to 500 ppm (245 mg Sn/L) in drinking water. The offspring behavioural assessments again included the runway task (PND 11), motor activity habituation (PND 17) and Morris water maze (as adults).

The results of Experiment 1 showed that there were no effects on any measure of growth, development, cognitive function or apoptosis following exposure to the test substance. There was a trend towards decreased brain weight in the high dose group. In addition, there was vacuolation of the neuropil in a focal area of the cerebral cortex of the adult offspring in all dose groups (1 -3 rats per treatment group).

In the second study, exposed females consumed significantly less water than the controls throughout both gestation and lactation, although neither dam nor pup weights were affected. As in Experiment 1, exposure did not alter pup runway performance, motor activity or cognitive function. These results indicate that perinatal exposure to the test substance, even at concentrations which decrease maternal fluid intake, does not result in significant neurobehavioral or cognitive deficits. While mild histological lesions were observed in the brain of adult offspring, the biological significance of this restricted finding in unclear.

In a private communication [Moser, 2007] the author reiterated the lack of any reproductive effects in either study. She further indicated that it was uncertain if the brain changes in adult rats referred to in the published article were adverse. These findings did not appear in offspring at PND 1, 12, or 22, did not affect cognitive function as measured within the study.

Discussion

In the weight-of-evidence analysis, maternal toxicity was evidenced by a slight indication of thymic involution and detriments in body weight and feed consumption at the highest dose in the OECD 421 study. Postnatal loss occurred at the highest dose in the OECD 421 study, but in the two more robust studies the postnatal loss could not be replicated, even at higher doses. The DNT studies clearly indicate that there are no reproductive effects of MMTC. Therefore, the weight-of-evidence analysis supports the conclusion that No Classification for reproductive toxicity is the appropriate decision.

Justification for classification or non-classification

In accordance with the criteria for classification as defined in Annex I, Regulation (EC) No 1272/2008, the substance does not require classification with respect to reproductive and developmental toxicity. However, in accordance with Annex VI of the Regulation, the substance has a harmonised classification and as such must be classified as a reproductive toxicant Category 2 (H361: Suspected of damaging fertility or the unborn child).