Methyl dihydrogen phosphate

Endpoint summary

Description of key information

The NOAEL for maternal toxicity was considered to be 120 mg/kg bw/day and 450 mg/kg bw/day for males for a similar multi-constituent substance. In combination with severe maternal toxicity observed at 450 mg/kg bw/d an increase in pup loss at birth and a decreased litter weight was noted in the high dose group. These developmental effects are considered to be caused by the maternal toxicity at 450 mg/kg bw/d. The developmental NOAEL is set at 120 mg/kg bw/day (OECD 422).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

not specified

GLP compliance:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

A total of 90 Wistar Hannover (Crl:WI(Glx/BRL/Han)IGSBR) rats (45 males and 45 virgin females), 9 to 10 weeks old and weighing 225 to 250 g for males and 176 to 200 g for females, were ordered from Charles River Italia S.p.A., Calco (Lecco), Italy. After arrival, on 13 September 2012, the weight range for each sex was determined and the animals were temporarily identified within the cage by means of a coloured mark on the tail. Body weight ranges were 238 to 253 g for males and 175 to 194 g for females. A health check was then performed by a veterinarian. An acclimatisation period of approximately 2 weeks was allowed before the start of treatment, during which time the health status of the animals was assessed by thorough observations. Animal room controls were set to maintain temperature and relative humidity at 22 ± 2°C and 55 ± 15% respectively; actual conditions were monitored, recorded and the records retained. No relevant deviations from these ranges were recorded during the study. There were approximately 15 to 20 air changes per hour and the rooms were lit by artificial light for 12 hours each day

Route of administration:

oral: gavage

Vehicle:

other: purified water

Details on oral exposure:

The test item was administered orally by gavage at a dose volume of 5 mL/kg body weight. Control animals received the vehicle alone at the same dose volume. The required amount of the test item was dissolved in the vehicle, purified water. The formulations were prepared daily (concentrations of 10, 24 and 90 mg/mL). Concentrations were calculated and expressed in terms of test item as supplied.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The proposed formulation procedure for the test item was checked during the pre-treatment period in the range of 10 to 90 mg/mL by chemical analysis (concentration) to confirm that the method was acceptable. Final results for all levels were within the acceptability limits stated in RTC SOPs for concentration (95-105%). Samples of the formulations, prepared on Weeks 1 and 6, were analysed to check the concentration. Results of the analyses were within the acceptability limits stated in RTC SOPs for concentration of solutions (95 to105%).

Duration of treatment / exposure:

Males
Animals were dosed once a day, 7 days a week, for a minimum of 2 consecutive weeks prior to pairing and thereafter through the day before necropsy.
Dose volumes were adjusted once per week for each animal according to the last recorded body weight.

Females
Animals were dosed once a day, 7 days a week, for a minimum of 2 consecutive weeks prior to pairing and thereafter during pairing, post coitum and post partum periods until Day 3 post partum or the day before sacrifice. Dose volumes were adjusted once per week for each animal according to the last recorded body weight.
During the gestation period, dose volumes were calculated according to individual body weight on Days 0, 7, 14 and 20 post coitum and on Day 1 post partum. Thereafter individual dose volumes remained constant.

Frequency of treatment:

Daily

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose:

Four groups comprised of 10 male and 10 female rats receive the test item at the dose levels of 0, 50, 120, 450 mg/kg/day

Control animals:

yes, concurrent vehicle

Details on study design:

Dose levels were selected in consultation with the Sponsor based on information from preliminary studies.

Observations and examinations performed and frequency:

Mortality

Throughout the study, all animals were checked early in each working day in the morning and in the afternoon. At weekends and public holidays a similar procedure was followed except that the final check was carried out at approximately mid-day.

Clinical signs

Once before commencement of treatment and at least once daily during the study, each animal was observed and any clinical signs recorded. Observations were performed at the same time interval each day, the interval was selected taking into consideration the presence of post-dose reactions.

Clinical observations (Functional Observation Battery Tests)

Once before commencement of treatment and at least once a week thereafter, each animal was given a detailed clinical examination. Each animal was removed from the home cage and observed in an open arena. The tests included observation of changes in gait and posture, reactivity to handling, presence of clonic or tonic movements, stereotypies or bizarre behaviour and effects on the autonomic nervous system (e.g. lachrymation, piloerection, pupil size, unusual respiratory pattern). All observation were performed for individuals animals.

Grip strength and sensory reactivity to stimuli

Once during the study, towards the end of treatment, 5 males and 5 females were randomly selected from each group for evaluation of sensory reactivity to stimuli of different modalities (e.g. auditory, visual and proprioceptive stimuli) and for assessment of grip strength. Measurements were performed using a computer generated random order.

Motor activity assessment (MA)

Once during the study, towards the end of treatment, 5 males and 5 females were randomly selected from each group and the motor activity was measured (for approximately 5 minutes) by an automated activity recording device. Measurements were performed using a computer generated random order

Body weight

Males were weighed weekly from allocation to termination.
Females were weighed weekly from allocation to positive identification of mating and on gestation Days 0, 7, 14 and 20. Dams were also weighed on Days 1 and 4 post partum

Food consumption

The weight of food consumed by each cage of males and females was recorded weekly (whenever possible) during the pre-mating period starting from allocation. Individual food consumption for the females was measured on gestation Days 7, 14 and 20 starting from Day 0 post coitum and on Day 4 post partum starting from Day 1 post partum.

Clinical pathology investigations

As a part of the sacrificial procedure, samples of blood were withdrawn under isofluorane anaesthesia from the abdominal vena cava from 5 males and 5 females (females with viable litters, if possible) randomly selected from each group, under condition of food deprivation.
The blood samples collected were divided into tubes as follows:

EDTA anticoagulant for haematological investigations
Heparin anticoagulant for biochemical tests
Citrate anticoagulant for coagulation tests

The measurements performed on blood samples are listed below:

Haematology

Haematocrit
Haemoglobin
Red blood cell count
Reticulocyte count
Mean red blood cell volume
Mean corpuscular haemoglobin
Mean corpuscular haemoglobin concentration
White blood cell count
Differential leucocyte count
- Neutrophils
- Lymphocytes
- Eosinophils
- Basophils
- Monocytes
- Large unstained cells
Platelets

Coagulation tests

Prothrombin time

Clinical chemistry

Alkaline phosphatase
Alanine aminotransferase
Aspartate aminotransferase
Gamma-glutamyltransferase
Urea
Creatinine
Glucose
Triglycerides
Bile acids
Phosphorus
Total bilirubin
Total cholesterol
Total protein
Albumin
Globulin
A/G Ratio
Sodium
Potassium
Calcium
Chloride

Urinalysis (only males)

At the same time interval of the clinical pathology investigations, individual overnight urine samples were also collected from the same animals under the same conditions. Before starting urine collection, water bottles were removed from each cage and each animal received approximately 10 mL/kg of drinking water by gavage, in order to obtain urine samples suitable for analysis.

Appearance
Volume
Specific gravity
pH
Protein
Glucose
Ketones
Bilirubin
Urobilinogen
Blood
The sediment, obtained from centrifugation at approximately 3000 rpm for 10 minutes, was examined microscopically for:

Epithelial cells
Leucocytes
Erythrocytes
Crystals
Spermatozoa and precursors

Sacrifice and pathology:

Parental animals sacrificed for humane reasons and those that had completed the scheduled test period were killed by exsanguination under isofluorane anaesthesia.

Parental males:
The males were killed after the mating of all females.

Parental females:
The females with live pups were killed on Day 4 post partum.
One high dose female with all pus stillborn (animal no. 93560069) was killed on Day 0 post partum and another high dose female (animal no. 93560073) was killed for humane reasons on Day 0 post partum.
The females which did not give birth 25 days after positive identification of mating (animal nos. 93560019, 93560023, 93560079) were sacrificed on Days 26, 27 or 27 post coitum.

Necropsy

The clinical history of the males and females of the parental generation was studied and a detailed post mortem examination was conducted (including examination of the external surface and orifices).
Changes were noted, the requisite organs weighed (excluding animals sacrificed for humane reasons or found dead) and the required tissue samples preserved in fixative and processed for histopathological examination.

Females:
All females were examined also for the following:

a) number of visible implantation sites (pregnant animals);
b) number of corpora lutea (pregnant animals).

Organ weights

From all animals completing the scheduled test period, the organs were dissected free of fat and weighed.
The ratios of organ weight to body weight were calculated for each animal.

Tissues fixed and preserved

Samples of all the tissues were fixed and preserved in 10% neutral buffered formalin (except eyes, optic nerves and Harderian glands, testes and epididymides which were fixed in modified Davidson's fluid and preserved in 70% ethyl alcohol).

Statistics:

Standard deviations were calculated as appropriate. For continuous variables the significance of the differences amongst group means was assessed by Dunnett’s test or a modified t test, depending on the homogeneity of data.
Statistical analysis of histopathological findings was carried out by means of the non-parametric Kolmogorov-Smirnov test if n was more than 5.
The non-parametric Kruskal-Wallis analysis of variance was used for the other parameters. Intergroup differences between the control and treated groups was assessed by the non-parametric version of the Williams test

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Three high dose females were found dead and 2 high dose females were sacrificed for humane reasons.

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Tracheal changes suggested to be related to treatment.

Other effects:

not examined

Details on results:

Mortality and fate of females:
Three high dose females (nos. 93560063, 93560067 and 93560071) were found dead during the study, on Days 21 and 15 post coitum and Day 12 of treatment, respectively.
The cause of deaths is suggested to be potentially related to the irritant properties of the test compound.
In addition, 2 high dose females (nos. 93560073, 93560069) were sacrificed for humane reason on Day 0 post partum.

Clinical observations (Functional Observation Battery Tests), Neurotoxicity assessment (removal of animals from the home cage and open arena):
Observation of animals at removal from the cage and in an open arena (neurotoxicity assessment) did not reveal changes attributable to the test item.

Clinical signs:
No significant clinical signs were noted in the males and in the surviving females, with the exception of one low dose not pregnant female, which showed piloerection, pallor and red staining in cage tray on Days 24/25 post coitum and one high dose pregnant female which showed hunched posture, respiratory distress and red staining on mounth and urogenital region (Day 0 post partum)

Body weights:
Body weights of males were unaffected by treatment.
No changes were observed in the body weight of females during pre-mating and post coitum periods. A very slight, not significant at statistical analysis, reduction in body weight was observed in the high dose females on Day 4 post partum when compared to controls (-10%).

Food consumption:
Food consumed was comparable between the control and treated groups.

Motor activity and sensory reactivity to stimuli:
No relevant differences in motor activity, grip strength and sensory reactivity to stimuli were observed.

Haematology:
No changes of toxicological significance were observed.
The statistically significant differences between males dosed with 50 mg/kg/day and controls (haematocrit and leucocytes) were considered to be incidental.
A slight increase of erythrocytes, haemoglobin and haematocrit and slight leucopenia were recorded in female no. 93560079. These findings were considered of no toxicological relevance.

Coagulation:
No changes were recorded.

Clinical chemistry:
Changes of a number of parameters, mainly metabolic markers, were observed in animals from all treated groups, with no dose-relation.
Males dosed with 450 mg/kg/day showed a slight increase of triglycerides (43%), phosphorus (19%) and bile acids (283%). Bile acids were also increased in some animals dosed with 50 and 120 mg/kg/day (165% and 65%, respectively), with no dose-relation.
In addition, animal no. 93560022 (50 mg/kg/day) showed moderate increase of transaminase enzymes. This finding was considered unrelated to treatment.
Treated females showed decrease of triglycerides (44% to 58%), cholesterol (18% to 28%), urea (20% to 22%), phosphorus (11% to 18%) and potassium (17% to 24%) and increase of glucose (10 to 27%).

Urinalysis only males:
No changes were recorded.

Terminal body weight and organ weights:
No treatment-related changes were observed in the weight of the organs in either sexes.
Terminal body weight was unaffected by treatment

Macroscopic observations:
No treatment-related changes were noted.

Microscopic observations:
In a single female rat treated with the high dose, tracheal minimal subchronic inflammation in the submucosa associated with minimal mucosal hyperplasia, was noted. The tracheal changes are suggested to be related to the irritant properties of the test compound.

Spermatogenic cycle:
Evaluation of the spermatogenic cycle did not show differences between the groups. Regular layering in the germinal epithelium was noted.

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

female

Basis for effect level:

other: pregnant females

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

male

Basis for effect level:

other: highest dose tested

Critical effects observed:

no

Conclusions:

The NOAEL for maternal toxicity was considered to be 120 mg/kg bw/day. In combination with severe maternal toxicity observed at 450 mg/kg bw/d an increase in pup loss at birth and a decreased litter weight was noted in the high dose group. These developmental effects are considered to be caused by the maternal toxicity at 450 mg/kg bw/d. The developmental NOAEL is set at 120 mg/kg bw/day.

Executive summary:

Study design 

The toxic effects on rats of both sexes after repeated dosing with Reaction mass of methyl dihydrogen phosphate and orthophosphoric acid and dimethyl hydrogen phosphate, as well as any effects of the test item on male and female reproductive performance, such as gonadal function, conception, parturition and early lactation of the offspring were investigated.

The vehicle was purified water. All doses were administered at a constant volume of 5 mL/kg body weight.

Males were treated for 2 weeks prior to pairing and during pairing with females until the day before necropsy, for a total of 32/33 days.

Females were treated for 2 weeks prior to pairing, during pairing and throughout the gestation and lactation periods until Day 3post partum or the day before necropsy.

The following investigations were performed in all groups: body weight, clinical signs (including neurotoxicity assessment, motor activity and sensory reaction to stimuli), food consumption, oestrous cycle, mating performance, clinical pathology investigations (haematology, clinical chemistry and males urinalysis), litter weight, pups observations, macroscopic observations and organ weights.

External examination for pups at Day 4 of lactation and external and internal examination in pups found dead were also performed. 

The histopathological examination was performed on control and high dose groups (five males and five females randomly selected). The examination included also the identification of the stages of the spermatogenic cycle.

Mortality and fate of females 

A total of 3 high dose females were found dead during the study and the cause of death is suggested to be potentially related to the irritant properties of the test compound. In addition, 2 high dose females were sacrificed for humane reasons on Day 0 post partum.

A total of 3 females were found not pregnant at necropsy.

The number of females with live pups on Day 4 post partum was: 9 in each of the control and low dose groups, 10 in the mid-dose group and 4 in the high dose group.

 

Daily clinical signsand weekly clinical observations (Functional Observation Battery Tests)

No treatment-related clinical signs were noted in the males and in the surviving females.

Weekly functional observation battery tests were unaffected by treatment.

 

Body weight and body weight gain 

Body weights of males were unaffected by treatment.

No changes of toxicological relevance were observed in the body weight of females.

 

Food consumption 

No effects on food consumption were observed.

 

Motor activity and sensory reactivity to stimuli 

No differences of toxicological significance were seen.

 

Haematology 

No changes of toxicological significance were seen.

 

Coagulation

No changes were recorded.

 

Clinical chemistry 

Changes of a number of parameters, mainly metabolic markers, were observed in animals from all treated groups, generally with no dose-relation, and/or with opposite trend in the two sexes.

 

Urinalysis – males only 

No changes were observed.

 

Oestrous cycle, mating performance and reproductive parameters 

All surviving females mated. No treatment-related anomalies were noted in the oestrous cycle of the treated females when compared to controls.

The copulatory and fertility indices were similar among groups.

Pre-coital interval and the number of copulation plugs were unaffected by treatment.

 

Implantation, pre-birth loss data and gestation length of females 

No significant differences were found in the number of corpora lutea, implantations, gestation length and total litter size between control and treated groups.

An increase in pre-birth loss % was noted in mid- and high dose groups with respect to the controls.

 

Litter data and sex ratio of pups 

At birth, % pup loss was considerably increased in the high dose group with respect to the controls with a consequent reduction in live litter size. In addition, a slight decrease in litter weight was also detected in the high dose group on Days 1 and 4 post partum.

No significant differences in sex ratio were detected.

 

Clinical signs of pups 

Clinical signs of pups were comparable between treated and control groups. 

Necropsy findings in decedent or humane killed pups and in pups sacrificed on Day 4post partum 

No milk in stomach was observed at necropsy in the decedent and humane killed pups of control and treated groups.

No abnormalities were found in pups of control and treated groups sacrificed on Day 4.

 

Terminal body weight and organ weights 

No treatment-related changes were observed in the weight of the organs in either sexes.

Terminal body weight was unaffected by treatment.

 

Macroscopic observations 

No treatment-related changes were noted.

 

Microscopic observations 

In a single female rat treated with the high dose, tracheal minimal subchronic inflammation in the submucosa associated with minimal mucosal hyperplasia, was noted. The tracheal changes are suggested to be related to the irritant properties of the test compound.

 

Spermatogenic cycle

Evaluation of the spermatogenic cycle did not show differences between the groups. Regular layering in the germinal epithelium was noted.

 

Conclusions

 The NOAEL for maternal toxicity was considered to be 120 mg/kg bw/day. In combination with severe maternal toxicity observed at 450 mg/kg bw/d an increase in pup loss at birth and a decreased litter weight was noted in the high dose group. These developmental effects are considered to be caused by the maternal toxicity at 450 mg/kg bw/d. The developmental NOAEL is set at 120 mg/kg bw/d

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Critical effects were not observed in an oral OECD 422 study and classification for specific target organ toxicity under the criteria given by Regulation (EC) No. 1272/2008 is not required.