Ammonium dihydrogenorthophosphate

Endpoint summary

Description of key information

No study with ammonium dihydrogenorthophoshate is present. Based on a reliable oral OECD 422 study with diammonium hydrogenorthophoshate in rats, local effects were observed in the stomach at the lowest dose tested (250 mg/kg bw/day). However, the systemic NOAEL is determined to be 250 mg/kg bw/day based on horizontal banding of dental surface at mid dose (LOAEL), with effects on haematological and clinical chemistry parameters at highest dose level. The read-across rationale can be found in the category approach document attached in IUCLID Section 13 and is fully included in the CSR.

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

Remarks:

combined repeated dose and reproduction / developmental screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 December 2001 - 24 May 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

adopted 22.03.96

Deviations:

no

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Limited, Margate, Kent, England.
- Age at study initiation: 9-10 weeks
- Weight at study initiation: 298 to 386 g for males and 191 to 263 g for females
- Fasting period before study: not applicable
- Housing:Unless paired for mating, the animals were singly housed in RB3 modified cages consisiting of high density polypropylene bodies with lids and floors of stainless steel grid. These cages were suspended in batteries over trays lined with absorbent paper. RB3 modified cages were used throughout the study with the exception of reproductive subgroup females from Day 17 after mating, where RB3 solid-bottomed
cages were used.
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 16 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-23°C, except on 3 occasions during which the temperature was minimally 16 or 18°C and the target temperature range was re-established within 24 hours.
- Humidity (%): 40-70%, except on 1 occasion during which the humidity was minimally 16% and the target temperature range was re-established on the next day.
- Air changes (per hr): approximately 15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 12 December 2001 To: 10 February 2002

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
The formulation for Group 4 (150 mg/ml) was mixed by adding the required volume of vehicle (water purified by reverse osmosis) to the required
weight of DAP and magnetically stirring for up to 1 hour until a visibly homogenous brown suspension was formed. Formulation for Groups 3 and 2
were prepared by direct dilution of this suspension.

VEHICLE
- Concentration in vehicle: 25 - 75 - 150 mg/ml
- Amount of vehicle (if gavage): 10 ml/kg

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples of each formulation prepared for administration during Weeks 1,4 and 6 of the study were analysed using spectrophotometry for test material content and found to be satisfactory.

Duration of treatment / exposure:

Animals were divided between two subgroups (toxicity and reproductive subgroups).
Males of both subgroups and females of the toxicity subgroup were treated until termination during week 6 of treatment. Doses were administered to the reproductive subgroup females for two weeks prior to pairing, throughout pairing and gestation until Day 3 of lactation. Animals that were
in parturition at the time of dosing were not dosed that day. Control animals received the vehicle over the same treatment period.
Animals were not dosed on their scheduled day of necropsy.

Frequency of treatment:

Daily

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

1 500 mg/kg bw/day (actual dose received)

No. of animals per sex per dose:

The toxicity subgroup consisted of 5 males and 5 females per group and the reproductive subgroup consisted of 10 females and
5 males per group.

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: As no treatment-related effects were seen on parameters assessed in a preliminary study at 1000 mg/kg/day, the high
dosage of 1500 mg/kg/day was selected by the Sponsor to attempt to elicit an overt toxic response and establish a reference level for toxicity.
The concept of a 'Limit Dose' is accepted by the OECD and is generally set in the region of 1000 mg/kg/day; therefore, it was not considered
necessary to investigate a dosage above 1500 mg/kg/day.

- Rationale for animal assignment (if not random): The animal numbers were assigned to groups in non-sequential manner due to the need for the
functional observation battery and detailed clinical signs to be performed without knowledge of the treatment groups to which animals were assigned.

- Section schedule rationale (if not random): The sequence in which the animals of the toxicity subgroup were killed after completion of the
observation period was selected to allow satisfactory inter-group comparison. Reproductive subgroup males were killed after the toxicity subgroup
animals and reproductive subgroup females were killed on Day 4 of lactation.

Positive control:

No.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily
- Cage side observations: evidence of reaction to treatment or ill-health

DETAILED PHYSICAL OBSERVATIONS: Yes
- Time schedule: weekly
- A more detailed physical examination was performed on each animal by an observer. After removal from the home cage, animals were
assessed for physical condition and behaviour during handling and after being placed in a standard arena. During these examinations particular
attention was paid to possible signs of neurotoxicity such as convulsions, tremor and abnormalities of gait or behaviour.

ADDITIONAL DETAILED OBSERVATIONS: Yes
- Time schedule: during Week 1 daily according to the following frequency:
1. Pre-dose observation, 2.As each animal was returned to its home cage, 3.At the end of dosing each group, 4.Between 1 and 2 hours after
completion of dosing all groups and 5.As late as possible in the working day.
From Week 2 to termination daily observations were limited to 1 and 4.

BODY WEIGHT: Yes
- Time schedule for examinations: Each male and toxicity subgroup female: on the day that treatment commenced, weekly thereafter, and at necropsy. Reproductive subgroup females: on the first day of treatment, weekly until pairing and on Days 0, 7, 14, 17 and 20 after mating, and Days 1 and 4 of
lactation, and at necropsy.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Time schedule for observations: All males and toxicity subgroup females: weekly throughout the study with the exception of the males whilst in
pairing with the reproductive subgroup females. Reproductive subgroup females: weekly before pairing then on Days 0,7,14, 17 and 20 after mating
and Days 1 and 4 of lactation. No food consumption was recorded for toxicity subgroup males or reproductive subgroup animals during pairing.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: During week 5, following FOB examinations
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes, overnight
- How many animals: toxicity subgroup animals (5 males + 5 females per dose group)
- Parameters checked: Haematocrit (Hct), Haemoglobin (Hb), Red blood cell count (RBC), Mean cell haemoglobin (MCH), Mean cell haemoglobin
concentration (MCHC), Mean cell volume (MCV), Total white cell count (WBC), Differential WBC count, Neutrophils (N), Lymphocytes (L), Eosinophils (E), Basophils (B), Monocytes (M), Large unstained cells (LUC), Platelet count (Pit), Reticulocyte count (Retic), Blood film for abnormal morphology and
unusual cell types, including normoblasts (The most common morphological changes, anisocytosis (aniscyto), micro/macrocytosis (Microcyto/
Macrocyto), hypo/hyperchromasia (Hypochrom/Hyperchrom), Platelet clumping (PIt. Clump)), Prothrombin time (PT) and Activated partial
thromboplastin time (APTT)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: During week 5, following FOB examinations
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes, overnight
- How many animals: toxicity subgroup animals (5 males + 5 females per dose group)
- Parameters checked: Alkaline phosphatase (ALP), Alanine aminotransferase (ALT), Aspartate aminotransferase (AST),
Gamma-glutamyl transpeptidase (gGT), Total Bilirubin (Bili), Urea, Creatinine (Creat), Glucose (Gluc), Total cholesterol (Chol), Sodium (Na),
Potassium (K), Chloride (Cl), Calcium (Ca), Inorganic Phosphorus (Phos), Magnesium (Mg), Total protein (Total Prot), Albumin (Alb),
Albumin/globulin ratio (A/G Ratio)

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: After 4 weeks of treatment
- Dose groups that were examined: Toxicity subgroup animals (5 males + 5 females per dose group)
- Battery of functions tested: Approach response, Touch response, Startle reflex (auditory), Tail pinch response, Grip strength: forelimb and
hindlimb and motor activity.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes, a detailed examination of the external features and orifices, the neck and associated tissues and the cranial, thoracic,
abdominal and pelvic cavities and their viscera.

Toxicity subgroup animals:
Animals were killed during Week 6 of treatment by carbon dioxide inhalation and subjected to a detailed necropsy.
The requisite organs were weighed after being dissected free of adjacent fat and other contiguous tissue. External and cut surfaces of the organs and tissues were examined as appropriate, abnormalities and interactions were noted and the required tissue samples and any abnormalities
preserved in appropriate fixative.
The following tissues were retained: Adrenals (left and right)*, Aorta - thoracic, Brain*, Caecum, Colon, Duodenum, Epididymides (left and right)*,
Eyes, Heart*, Ileum, Jejunum, Kidneys (left and right)*, Liver*, Lungs (including bronchi), Lymph nodes - mandibular, Lymph nodes - mesenteric,
Lymph nodes - regional to masses, Mammary area, Oesophagus, Optic nerves, Ovaries (left and right)*, Pancreas, Pituitary*, Prostate *, Rectum,
Salivary glands, Sciatic nerves, Seminal vesicles*, Skin, Spinal cord, Spleen*, Sternum (with bone marrow), Stomach, Testes (left and right)*,
Thymus*, Thyroids with parathyroids**, Trachea, Urinary bladder, Uterus with cervix*, Vagina
* Organ weight recorded / * * Organ weight recorded after fixation.

Reproductive subgroup animals:
Males were killed after the toxicity subgroup animals. They were subjected to a detai led necropsy for evidence of disease or adverse reaction to
treatment. The testes, epididymides, seminal vesicles with coagulating gland and prostate were retained for each animal. Females were killed on
Day 4 of lactation by carbon dioxide inhalation and subjected to a detailed necropsy for evidence of disease or adverse reaction to treatment.
The number of implantation sites was recorded and the ovaries, uterus with oviducts and cervix, vagina, pituitary and mammary tissue retained in appropriate fixative. Abnormal tissues were also retained in appropriate fixative. Offspring of the reproductive subgroup females were killed by
intraperitoneal injection of sodium pentobarbitone on Day 4 of age and subjected to a macroscopic necropsy. Abnormal tissues were also retained in appropriate fixative. Any offspring dying before scheduled termination were subjected to necropsy and assessment of the stomach for milk
content.

HISTOPATHOLOGY: Yes

Toxicity subgroup animals:
Organs (including abnormalities) preserved at macroscopic necropsy were processed for animals from the Control and high dosage groups
(Groups 1 and 4). Following treatment related findings in Group 4, the stomachs of intermediate and low dosage animals were also processed and examined. Tissue samples were dehydrated, embedded in paraffin wax and sectioned at approximately four to five micron thickness. Staining was with haematoxylin and eosin, except testes, which were stained with periodic acid/schiff (PAS).
The following tissues were scheduled for histopathology: Abnormalities, Adrenals (cortex and medulla), Aorta (thoracic), Brain (cerebrum,
cerebellum, midbrain), Caecum, Colon, Duodenum, Epididymides (longitudinal section to include the caput and cauda epididymides), Eyes
(longitudinal section of each (both examined)), Heart (including auricular and ventricular regions), Ileum, Jejunum, Kidneys (including cortex,
medulla and papilla regions), Liver (section from all main lobes), Lungs (section from two major lobes, to include bronchi), Lymph nodes,
Mammary area, Oesophagus, Ovaries, Pancreas, Pituitary, Prostate, Rectum, Salivary glands, Sciatic nerves (only one examined), Seminal vesicles,
Skin, Spinal cord (transverse and longitudinal sections at the cervical, thoracic and lumbar levels), Spleen, Sternum (with bone marrow),
Stomach (keratinised, glandular and antrum), Tissue (region to be examined (where appropriate)), Testes, Thymus, Thyroid (included parathyroid
in section, where possible), Trachea, Urinary bladder, Uterus (uterus section separate from cervix section (both examined)), Vagina.

For bilateral organs sections of both the left and right organs were examined. A separate section was prepared from each of the remaining tissues.

In addition to the general histopathological examination of all testicular elements, including tubular and interstitial compartments,
spermatogenesis was assessed taking into consideration the stages of the spermatogenic cycle. Where no disturbances were detected, the testes
were recorded as normal.

Reproductive subgroup animals:
Histology for reproductive subgroup animals was restricted to the retained reproductive organs and abnormalities observed at macroscopic
necropsy.

Other examinations:

Mating procedure:
All 10 males in each group (toxicity and reproductive subgroups) were mated with the 10 reproductive subgroup females after all animals had
received 2 weeks of treatment. Pairing was on a one-to-one basis within treatment groups for up to 2 weeks, although all animals mated and were
separated within 1 week.
Each morning, following pairing, the trays beneath the cages were checked for ejected copulation plugs and a wet vaginal smear was prepared from each female and examined for the presence of spermatozoa. The day on which a sperm positive vaginal smear or at least three copulation plugs
were found was designated Day 0 of gestation. Once mating had been confirmed, males and females were separated and the males were returned
to their normal group housing.

Parturition observations and gestation length:
From Day 20 after mating reproductive subgroup animals were checked 3 times daily for evidence of parturition. The females were permitted to
deliver their young naturally and rear their own offspring until Day 4 of lactation. Numbers of live and dead offspring were recorded during the
parturition process.

Offspring observations:
All offspring were examined at approximately 24 hours after birth (Day 1) and the number of offspring born (live and dead) was recorded.
Live offspring were individually identified within each litter by toe tattoo and any clinical observations were recorded.
Litters were observed daily for evidence of abnormal appearance or behaviour. Daily records were maintained of mortality and consequent
changes in litter size. Where practical, any offspring found dead were subjected to a macroscopic examination as soon as possible.
The offspring were sexed at individual weighing on Day 1 and Day 4 of age.

Statistics:

For some parameters, the similarity of the data was such that analyses were not considered to be necessary.
For categorical data, the proportion of animals was analysed using Fisher's Exact test.
For continuous data, Bartlett's test was first applied to test the homogeneity of variance between the groups. Using tests dependent on the outcome
of Bartlett's test, treated groups were then compared with the Control group, incorporating adjustment for multiple comparisons where necessary.
For bodyweight gains and organ weights, whenever Bartlett's test was found to be statistically significant, a Behrens-Fisher test was used to perform
pairwise comparisons, otherwise a Dunnett's test was used.
The following sequence of statistical tests was used for grip strength and motor activity, bodyweight change during gestation and lactation,
bodyweight and bodyweight change for offspring, food consumption and clinical pathology data:
- If 75% of the data were the same value, then a frequency analysis was applied. Treatment groups were compared using a Mantel test for a trend in
proportions and also pairwise Fisher's Exact tests for each dose group against the control.
- If Bartlett's test for variance homogeneity was not significant at the 1 % level, then parametric analysis was applied. If the F 1 test for monotonicity of dose-response was not significant at the 1 % level, Williams' test for a monotonic trend was applied. If the F 1 test was significant, Dunnett's test was
performed instead.
- If Bartlett's test was significant at the 1 % level, then logarithmic and square-root transformations were tried. If Bartlett's test was still significant, the non-parametric tests were applied. If the HI test for monotonicity of dose-response was not significant at the 1 % level, Shirley's test for a monotonic
trend was applied. If the HI test was significant, Steel's test was performed instead.

Significant differences were expressed at the 5% (p<0.05) or 1% (p<0.01) level.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

effects observed, treatment-related

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS AND MORTALITY: One toxicity subgroup female receiving 1500 mg/kg/day was found dead with findings that were consistent with a dosing error. This death was therefore considered to be unrelated to treatment.
A dosage-dependant increase in transient post-dosing salivation was apparent, and this was considered more likely to be due to the palatability of
the test formulations than to an effect of the test material. A dosage-dependant increase in the number of animals with reddening of the extremities
was also apparent mainly during the early stages of treatment.

BODY WEIGHT AND WEIGHT GAIN:
The body weight gain of males at 1500 mg/kg/day appeared to be suppressed when compared with Control, such that gain between Weeks 0-5 for
this group was 78% of Control. This parameter appeared to be unaffected for toxicity subgroup females or reproductive subgroup females before
pairing. Bodyweight gain for reproductive subgroup females receiving 1500 mg/kg/day was reduced during the first week of gestation, after which
values returned to Control-comparable levels through to termination at Day 4 of lactation.

FOOD CONSUMPTION:
Food consumption of males at 1500 mg/kg/day appeared to be marginally lower when compared with Control.
There were no effects of treatment on the amount of food consumed by females of both toxicity and reproductive subgroups.

FOOD EFFICIENCY:
Food conversion efficiency was low for toxicity subgroup males at 1500 mg/kg/day during Week 5 compared with the Control and other groups,
although values were generally variable.

HAEMATOLOGY:
There was a reduction in activated partial thromboplastin time for toxicity subgroup males at 750 and 1500 mg/kg/day (74 and 76% of control, resp.), although this was not dosage related. No treatment related changes in these parameters were observed for toxicity subgroup females. Reviewer considers this not toxicologically relevant at 750 mg/kg bw, due to no dose response, high standard deviation, no effects in the liver, control value very high (historical control data Charles River, hematology parameters for the Crl:CDBR Rat, 1993)..

CLINICAL CHEMISTRY:
The following changes were recorded among toxcicity subgroup males for which an effect of treatment could not be discounted:
a non dosage-dependant elevation of alkaline phosphatase levels at 750 and 1500 mg/kg/day (132 and 131% of control, resp.); reduced glucose and phosphorous levels at 1500 mg/kg/day (79 and 82% of control, resp.); a small but dosage-dependant reduction in total protein at 750 and
1500 mg/kg/day (93 and 91% of control, resp.) with a slightly elevated albumin/globulin ratio at the top dosage (117% of control). Changes in toxicity subgroup females were limited to a decrease in phosphorous levels at 1500 mg/kg/day (81% of control) although a non-significant increase in
alkaline phosphatase levels at 1500 mg/kg/day (122% of control) in particular suggested a similar change to that recorded in males.
Reviewer: Effect on total protein (at 750 mg/kg bw) although dose related was marginal (<10% compared to control), no change in albumin or A/G ratio and within the historical range of control data (Clinical Laboratory Parameters for Crl:CD(SD) rats, 2006, Charles River Laboratories).

ORGAN WEIGHTS:
Bodyweight relative kidney and liver weights for toxicity subgroup females at 1500 mg/kg/day were increased, but in the absence of a histological
correlate for these findings, this was of uncertain toxicological significance.

GROSS PATHOLOGY:
A number of toxicity subgroup males and females at 750 and 1500 mg/kg/day had thickened stomachs and associated findings.This is a local reversible effect according to the reviewer.
A number of toxicity subgroup males and females at 750 and 1500 mg/kg/day exhibited horizontal bands on the incisors.

HISTOPATHOLOGY: NON-NEOPLASTIC
Stomachs of toxicity subgroup animals showed minimal or slight submucosal inflammation at all doses (0/5, 3/5, 4/5 and 2/5 males and
0/5, 2/5, 4/5 and 4/5 females at 0, 250, 750 and 1500 mg/kg bw respectively). It is thought that these findings may have been associated with
an irritant effect of the test formulations rather than systemic toxicity.
Histological processing of the teeth that showed horizontal banding failed to detect any involvement of areas examined suggesting that the banding was probably restricted to the enamel of the teeth. This directs to an effect on the mineralisation process of tooth and bones. Reviewer: The roots of the teeth were not examined, so whether the cells that produce emaille are affected remains unknown.

OTHER FINDINGS:
Reproductive subgroup animals: Mating performance and fertility were unaffected by treatment, and parental treatment had no apparent effect on the
offspring to day 4 of age. The following parameters were unaffected by treatment: pre-coital interval, mating performance and fertility, gestation length and gestation index, litter size, offspring survival indices, sex ratio, offspring body weight and macropatholgy for offspring.

Key result

Dose descriptor:

NOAEL

Remarks:

systemic

Effect level:

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

Sex:

male/female

Basis for effect level:

other: general toxicity: horizontal banding of dental surface at mid dose (LOAEL), with effects on haematological and clinical chemistry parameters at highest dose level.

Key result

Dose descriptor:

NOAEL

Effect level:

>= 1 500 mg/kg bw/day (actual dose received)

Sex:

male/female

Basis for effect level:

other: reproduction/developmental toxicity

Critical effects observed:

not specified

Conclusions:

NOAEL: 250 mg/kg/day for general toxicity, since the local (slight to mild) stomach effects at 250 mg/kg are considered due to an irritant
rather than toxic effect of the test substance formulations.
NOAEL: 1500 mg/kg/day for reproduction/developmental toxicity.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

250 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The study has been performed according to OECD and/or EC guidelines and according to GLP principles.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No reliable study is present for ammonium dihydrogenorthophosphate.

In a reliable oral OECD 422 study, rats (5/sex/dose) were dosed 250, 750 and 1500 mg/kg bw/day diammonium hydrogenorthophoshate. Males and females were treated until termination during week 6 of treatment. The body weight gain of males at 1500 mg/kg/day appeared to be suppressed between Weeks 0 -5. There was a reduction in activated partial thromboplastin time for males at 750 and 1500 mg/kg/day, although this was not dosage related. No treatment related changes in these parameters were observed for females. Reviewer considers this not toxicologically relevant at 750 mg/kg bw, due to no dose response, high standard deviation, no effects in the liver, control value very high (historical control data Charles River, hematology parameters for the Crl:CDBR Rat, 1993). Males showed a non-dosage dependent elevation of alkaline phosphatase levels at 750 and 1500 mg/kg/day, reduced glucose and phosphorous levels at 1500 mg/kg/day, a small but dosage-dependant reduction in total protein at 750 and

1500 mg/kg/day with a slightly elevated albumin/globulin ratio at the top dosage. Changes in females were limited to a decrease in phosphorous levels at 1500 mg/kg/day although a non-significant increase in alkaline phosphatase levels at 1500 mg/kg/day in particular suggested a similar change to that recorded in males. Reviewer: Effect on total protein (at 750 mg/kg bw) although dose related was marginal (<10% compared to control), no change in albumin or A/G ratio and within the historical range of control data (Clinical Laboratory Parameters for Crl:CD(SD) rats, 2006, Charles River Laboratories). Therefore, not considered adverse.

Bodyweight relative kidney and liver weights for toxicity subgroup females at 1500 mg/kg/day were increased, but in the absence of a histological correlate for these findings, this was of uncertain toxicological significance. A number of males and females at 750 and 1500 mg/kg/day had thickened stomachs and associated findings, and exhibited horizontal bands on the incisors. Stomachs of animals showed minimal or slight submucosal inflammation at all doses (0/5, 3/5, 4/5 and 2/5 males and 0/5, 2/5, 4/5 and 4/5 females at 0, 250, 750 and 1500 mg/kg bw respectively). It is thought that these findings may have been associated with an irritant effect of the test formulations rather than systemic toxicity. Reviewer considers this a common local effect which is reversible.

Histological processing of the teeth showed horizontal banding failed to detect any involvement of areas examined suggesting that the banding was probably restricted to the enamel of the teeth. This directs to an effect on the mineralisation process of tooth and bones. Reviewer: The roots of the teeth were not examined, so whether the cells that produce emaille are affected remains unknown.Based on this a systemic NOAEL of 250 mg/kg bw/day is derived.

No dermal or inhalation toxicity studies are present. Although dermal exposure is likely, dermal absorption is considered to be very low and thus a dermal exposure study would be of limited value. In addition, the vapour pressure of the substance is assumed to be low and the particle sizes show that less than 10% of the particles is < 100 μm (inhalable fraction, see particle size distribution results), indicating that only very limited inhalation exposure is possible.

Based on an expert statement, no additional studies with ammonium dihydrogenorthophosphate are performed. Exposure to the ammonium cation from uses regulated under REACH is considered to be negligible compared to the natural abundancy of ammonium in humans and the effect to evaluate the safety of high levels of phosphate in the diets of animals are complicated by the need to separate the effect of the phosphate itself from the imbalance in the ratios of phosphate and other essential cations. It is not considered to be scientifically justified to conduct further in vivo testing for repeated dose toxicity as the current available information is both sufficient for characterization of the hazard profile of the substance upon repeated dose exposure and for the performance of a chemical safety assessment for repeated dose toxicity.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
One 28-day study on the read-across substance diammonium hydrogenorthophoshate is available.

Justification for classification or non-classification

Based on the available data, ammonium dihydrogenorthophosphate does not have to be classified for general toxicity according to Regulation (EC) No. 1272/2008 on Classification&Labelling.