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Acute Toxicity: inhalation

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acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
No data
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:

In accordance with REACH Annex XI, Section 1.5, of Regulation (EC) No. 1907/2006 (REACH) the standard testing regime may be adapted in cases where a grouping or read-across approach has been applied.

The similarities may be based on:
(1) a common functional group
(2) the common precursors and/or the likelihood of common breakdown products via physical or biological processes, which result in structurally similar chemicals; or
(3) a constant pattern in the changing of the potency of the properties across the category
Diammonium dihydrogenpyrophosphate is a soluble inorganic salt consisting of pyrophosphate anions and ammonium cations. Similarities between the source chemical (sodium acid pyrophosphate) and the target chemical (diammonium dihydrogenpyrophosphate) are based on the following:
(1) The source chemical (sodium acid pyrophosphate) and the target substance (diammonium dihydrogenpyrophosphate) are structurally similar substances. Both are soluble inorganic phosphate salts. In vivo both substances will be (bio)transformed into their respective ionic forms; phosphate anions (either diphosphate or orthophosphate depending on degree of metabolism) and cations; either ammonium or sodium. Exposure to the non-common compound, the sodium ion, will not result in toxicological effects at the dose levels tested. Similarly, the effects of different phosphate moieties are not considered to be toxicologically significant due to in vivo (bio) transformation.
(2) Both substances contain the bio transformation product: orthophosphate. Pyrophosphate will ultimately be converted to orthophosphate in vivo. The key moiety for the assessment of diammonium dihydrogenpyrophosphate is the ammonium cation and as such the effects of the target compound (diammonium dihydrogenpyrophosphate) are expected to be equal to or worse than the effects of the source substance (sodium acid pyrophosphate) for the property under consideration.
See read-across justification report attached.

See read-across justification report attached.

See read-across justification report attached.

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guidelineopen allclose all
according to guideline
EPA OPP 81-3 (Acute inhalation toxicity)
- minor deviations: the chamber and room humidity was slightly higher than recommended in the guideline
according to guideline
OECD Guideline 403 (Acute Inhalation Toxicity)
- minor deviations: the chamber and room humidity was slightly higher than recommended in the guideline
according to guideline
EU Method B.2 (Acute Toxicity (Inhalation))
- minor deviations: the chamber and room humidity was slightly higher than recommended in the guideline
GLP compliance:
yes (incl. QA statement)
Test type:
standard acute method
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
Disodium dihydrogenpyrophosphate
EC Number:
EC Name:
Disodium dihydrogenpyrophosphate
Cas Number:
Molecular formula:
disodium [hydroxy(oxido)phosphoryl] hydrogen phosphate
Details on test material:
Name of test material (as cited in study report): Sodium acid pyrophosphate
Analytical purity: No data

Test animals

Details on test animals or test system and environmental conditions:
- Source: Charles River Laboratories, Kingston, NY
- Age at study initiation: The actual age of the rats was not specified, only that they were young adults.
- Weight at study initiation (± SD): Males: 318 ± 11.4 g; Females: 249 ± 12.6 g
- Fasting period before study: No data
- Housing: Animals were housed individually in stainless steel suspended rat cages. Deosorb bedding was used in the litter pans.
- Diet: Purina Laboratory Rodent Chow 5001 available ad libitum
- Water: Tap water available ad libitum
- Acclimation period: Minimum of 5 days

- Temperature (°C): 21 - 23 °C (quoted in the study as 69 - 74 °F)
- Humidity (%): 42 - 77%
- Air changes (per hr): 14.2 air changes per hour
- Photoperiod (hrs dark / hrs light): 12 h fluorescent light and 12 h dark cycle

Administration / exposure

Route of administration:
inhalation: dust
Type of inhalation exposure:
whole body
other: unchanged (no vehicle)
Details on inhalation exposure:
- Exposure apparatus: The Rochester type exposure chamber was made of stainless steel and glass and was operated dynamically. The calculated 99% equilibrium time for the chamber at a flow rate of 35.6 L per minute was 19.4 minutes (equivalent to 14.2 "air changes per hour").
- Exposure chamber volume: 150 L
- Method of holding animals in test chamber: The test animals were assigned to and housed in individual compartments of a wire mesh cage bank (all on the same horizontal level) during the exposure.
- Source and rate of air: Breathing grade compressed air was used and the total chamber air flow rate was 35.6 L/minute.
- Method of conditioning air: No data
- System of generating particulates/aerosols: The test material was generated using a BGI Wright Dust Feeder II. The test material was desiccated and packed into large dust cups. Breathing Grade compressed air was metered to the Wright dust feeder through teflon tubing by a Matheson® 605 rotameter with a metal float. Rotameter back pressure was controlled using a Matheson® 3104C regulator. The dust feeder back pressure was monitored using a Marshalltown® back pressure gauge. The test material was made airborne by the compressed air dispersing the material into the exposure chamber. The concentration of the test atmosphere was controlled by the delivery rate setting of the Wright dust feeder.
- Method of particle size determination: The samples were drawn through a Sierra 218 cascade impactor at 2.78 liters per minute. The aerodynamic particle size distribution was determined by gravimetric analysis of the amount of test material collected on the impactor stages and subsequent determination of the mass median aerodynamic diameter (MMAD), geometric standard deviation and other particle size parameters by logarithmic-probability plotting.
- Treatment of exhaust air: The chamber air was exhausted from the bottom of the chamber and passed through an orifice tube system which continuously monitored airflow and then through a commercial filter box. The filter box was connected to a line leading to additional filters and an exhaust fan on the roof. The exhaust operated at a flow rate of 35.6 liters per minute, creating a slight negative pressure in the chamber, which was considered to be the total chamber air flow rate. The entire exposure system and primary exhaust filter were contained in a fume hood.
- Temperature, humidity, pressure in air chamber: The mean temperature and relative humidity in the chamber were 22 °C (71 °F) and 66%, respectively. The pressure in the air chamber was not measured.

- Brief description of analytical method used: The airborne concentration of the test material was determined gravimetrically.
- Samples taken from breathing zone: Yes - Chamber air samples were taken on glass fiber filters held in cassettes at approximately one hour intervals during the exposure to determine the airborne concentration of test material. The airborne concentration of the test material was determined gravimetrically by drawing a known amount of chamber air through the filter. The samples were taken from the center of the chamber directly over the animal exposure caging.
The difference between gravimetric and nominal concentration was attributed to sedimentation of larger particles and/or adhesion of the test material to surfaces in the exposure chamber.

- Not applicable: The test material was administered as received and a vehicle was not used.

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution: The fraction of particles less than or equal to 1 µm in mass aerodynamic diameter, based on the log-probability graphs, ranged from 7.6 to 9.4%. The fraction of particles less than or equal to 10 µm in mass aerodynamic diameter, based on the log probability graphs, ranged from 72.3 to 76.1%. These results indicated the test material was respirable in size to the rat.
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): The MMADs ranged from 4.61 to 4.87 micrometers (µm) with geometric standard deviations ranging from 2.98 to 3.39. The MMAD represents the smallest size that could be achieved in this study. The material is hygroscopic causing the particles to agglomerate and/or adhere to surfaces inside the chamber. Several trials were initially performed with various generation schemes and the system which was ultimately chosen provided the best performance.
Analytical verification of test atmosphere concentrations:
Duration of exposure:
4 h
Nominal concentration: 35.14 mg/L (maximum attainable concentration)
Gravimetric concentration: 0.58 ± 0.103 mg/L
No. of animals per sex per dose:
5 animals/sex
Control animals:
Details on study design:
- Duration of observation period following administration: 28 days
- Frequency of observations and weighing: Animals were observed for signs of toxicity and mortality every 15 mins during the first hour of exposure, hourly for the remainder of the exposure, upon removal from the chamber, at 1 h post-exposure, twice daily thereafter for 27 days and once on day 28. Individual body weights were recorded on days 0, 1, 2, 4, 7, 14, 21 and 28.
- Necropsy of survivors performed: Yes
- Other examinations performed: No data
No data

Results and discussion

Preliminary study:
Not applicable
Effect levels
Dose descriptor:
Effect level:
> 0.58 mg/L air (analytical)
Exp. duration:
4 h
See Table 1.
One female died on day 1 and one male died on day 14 post-exposure.
Clinical signs:
other: See Table 1. Clinical signs noted during the exposure included lacrimation, material on fur, oral discharge and squinting eyes. Incidence of clinical signs was highest at the removal from chamber observation. Signs gradually resolved during the study, how
Body weight:
See Table 2.
Most animals lost weight through day 4 of the study, then began to gain weight in a normal pattern. At termination all surviving animals exhibited increases in body weight over their day 0 values.
Gross pathology:
See table 3.
There were no gross internal lesions observed in any animal which survived to study termination. One male which died on day 14 had discoloured lungs with many light red nodules. This animal was also observed to have a corneal opacity in one eye.
Other findings:
No data

Any other information on results incl. tables

See attached file for Tables 1, 2 and 3.

Applicant's summary and conclusion

Interpretation of results:
GHS criteria not met
Under the conditions of this study, the test material caused mortality in one male and one female Sprague Dawley rat when administered for four hours at a mean, maximum attainable chamber concentration of 0.58 mg/L. Based on this, the LC50 for sodium acid pyrophosphate is considered to be greater than 0.58 mg/L.
This study is considered to be acceptable and to adequately satisfy both the guideline requirement and the regulatory requirement as a key study for this endpoint. In addition the study is considered to be acceptable for classification and labelling in accordance with Regulation (EC) No 1272/2008 (EU CLP) and as such sodium acid pyrophosphate is not considered to be acutely toxic via the inhalation route (EU CLP).