Registration Dossier

Administrative data

acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 12th of April, 1991 to 28th of May, 1991
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted according to OECD guideline N°403 in compliance with GLP Substance identification: isohexadecan as mixture of C16 isoparaffins Substance analytical certificate not available
Cross-referenceopen allclose all
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
according to
OECD Guideline 403 (Acute Inhalation Toxicity)
Substance identification: isohexadecane as mixture of C16 isoparaffins; substance analytical certificate not available
Principles of method if other than guideline:
guideline study
GLP compliance:
Test type:
standard acute method
Limit test:

Test material

Details on test material:
- Name of test material (as cited in study report): Isohexadecan
- Substance type: Petroleum product, UVCB
- Physical state: liquid, gas, colorless
- Analytical purity: 100% commercial product
- Composition of test material, percentage of components: mixture of C16 Isoparaffins (93685-80-4)
- Lot/batch No.: production from 03.04.1991
- Stability under test conditions: stable

Test animals

Details on test animals and environmental conditions:
- Source: BRL, Biological Research Laboratories Ltd, CH-4414 Fuellinsdorf/Switzerland
- Age at study initiation: males: 8-10 weeks; females: 10-12 weeks
- Weight at study initiation: males: 180.0-200.0 g; females: 181.0-199.6 g
- Housing: Makrolon type-4 cages with wire mesh tops and standard softwood bedding
- Diet (e.g. ad libitum): pelleted Kliba 343, batches nos 83/91 and 85/91, ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: From 5 to 11 days under laboratory conditions after clinical health examination

- Temperature (°C): 22 ± 3°C
- Humidity (%): 30-70%
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 12 April 1991 To: 28 May 1991

Administration / exposure

Route of administration:
other: droplets aerosol
Type of inhalation exposure:
nose only
other: air
Details on inhalation exposure:
The test substance was in an automatic syringe pump feeding a nebulizer. The test atmosphere generated by the nebulizer was then diluted with clean air to achieve the concentrations required for the study with a target median aerodynamic diameter of 3 µm or less and discharged into the exposure chamber. The test substance was used as supplied and generated by nebulisation.

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION: inhalation exposure system according to Sachsse et al. (1973, 1976)
- Exposure apparatus: Sachsse et al. (1973, 1976)
- Exposure chamber volume: 0.7 L
- Method of holding animals in test chamber: animals were maintained in a tube for nose-only inhalation
- Source and rate of air: 10-15 air changes per hour
- Method of conditioning air: no data
- System of generating particulates/aerosols: nebulizer
- Method of particle size determination: Mercer 7 stage cascade impactor
- Treatment of exhaust air: no data
- Temperature, humidity, pressure in air chamber: 22 ± 3°C, relative humidity of 30-70%

- Brief description of analytical method used: test substance was sampled and passed through three wash bottles of isooctane and cooled to -70°C. The content of each wash bottle was transfered into 100 mL volumetric flasks, the bottles were rinsed with isooctane and the flasks filled up to 100 mL with the rinsing. Aliquots were analysed by gas chromatography according to a method provided by the sponsor.
- Samples taken from breathing zone: yes

VEHICLE : No vehicle

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution:cumulative % of particles mass <= 3 µm between 62.0 to 49.8%
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): 1.66/2.55 at 1.22 mg/L; 3.30/2.17 at 3.53 mg/L; 3.04/1.94 at 6.06 mg/L

Analytical verification of test atmosphere concentrations:
See below "Concentrations"
Duration of exposure:
4 h
Nominal concentrations: 1.22 mg/L air - 3.53 mg/L air - 6.06 mg/L air
Gravimetric concentrations: 0.55 ± 0.18 mg/L air ; 2.38 ± 0.23 mg/L air; 5.14 ± 0.12 mg/L air
Analytical concentrations: 0.63 ± 0.10 mg/L air; 2.03 ± 0.15 mg/L air; 4.41 ± 0.27 mg/L air
No. of animals per sex per dose:
5/sex/dose (see below Table 7.2.2/1)
Control animals:
Details on study design:
- Duration of observation period following administration: 15 days
- Frequency of observations and weighing: mortality: once per hour during exposure, once after exposure on test day 1, and twice daily thereafter
* Bodyweights: on day 1 (before exposure) 8 and 15 of test using a Mettler PM 4000 balance.
* Clinical signs: Once per hour during exposure (only grossly abnormal signs, as the animals were in restraint tubes), once after exposure and once daily thereafter.
- Necropsy of survivors performed: yes
- Other examinations performed: macroscopic changes or abnormalities were described during necropsy. Lungs, trachea, larynx, and nasopharyngeal tissues were collected from all animals and fixed. The organs with macroscopic pathological changes were fixed similarly.
LOGIT-Model for LC50 calculation

Results and discussion

Preliminary study:
Not applicable
Effect levelsopen allclose all
Dose descriptor:
Effect level:
1.85 mg/L air
95% CL:
Exp. duration:
4 h
Dose descriptor:
Effect level:
1.68 mg/L air
95% CL:
1.47 - 1.91
Exp. duration:
4 h
Dose descriptor:
Effect level:
1.73 mg/L air
95% CL:
1.54 - 1.94
Exp. duration:
4 h
In group 2, one male and one female died during exposure (4-hour exposure). The other two males and three females of this group died between test days 1 and 2 after exposure. In group 3, three males and two females died during exposure; the other two males and two females died between test days 1 and 2.
Clinical signs:
other: Restlessness was observed in a few animals of all groups during exposure. Group 1: hunched posture (one male, on test-day 1 only) Group 2: sedation, apathy, ventral recumbency, hunched posture up to test day 3 in the surviving female and up to test day
Body weight:
No treatment-related effects on body weights were noted in animals of group 1 nor in surviving animals of group 2 or 3.
Gross pathology:
Group 1: the lungs of 4 males and all females were incompletely collapsed. Isolated dark red foci were noted on the right cranial lobes of two males.
Group 2: the lungs of all males and all females were either incompletely or not collapsed with a dark red or reddish discoloration in 7 cases. Isolated to several gray-white foci were noted on the eyes of 2 males. A foamy fluid released from the bronchi was observed in 1 male and 1 female. The eyes of 2 females showed a gray white discoloration.
Group 3: the lungs of all males and 4 females were incompletely collapsed and showed a gray-white discoloration.
Other findings:
No additional data

Any other information on results incl. tables

No additional data

Applicant's summary and conclusion

Interpretation of results:
Migrated information Criteria used for interpretation of results: EU
Under the test conditions, isohexadecan is classified as harmful by inhalation according to the criteria of Annex VI to the Directive 67/548/EEC and category 4 in CLP Regulation 1272/2008.
Executive summary:

C16 Paraffins were tested for acute toxicity by inhalation in Wistar rats according to OECD guideline N°403 in compliance with GLP. Groups of animals (5 males and 5 females) were exposed for 4 hours to the test substance as an aerosol at a delivery flow concentration of 0.63 mg/L, 2.63 mg/L or 4.41 mg/L of air with a target median aerodynamic diameter of 3 µm or less and discharged into the exposure chamber.

Examinations for mortality, clinical signs and body weight gain were performed during the 14-day observation period. All surviving animals were necropsied at the end of the observation period.

No deaths occurred in group of animals exposed to the aerosol lowest concentration (group 1) while mortality of 70% and 90% was observed in the middle and the highest dose group, respectively. The lungs of all males and all females exposed at the middle concentration showed either incompletely or not collapsed with a dark red or reddish discoloration in 7 cases. Isolated to several grey white foci were noted on the eyes of two males while a grey white discoloration of eyes was observed in two females. In the highest concentration group, the lungs of all males and 4 females were incompletely collapsed and showed a grey-white discoloration.

The LC50 was 1.85 mg/L air in males, 1.68 mg/L air for females and 1.73 mg/L air for both sexes. Thus, isohexadecan is classified as harmful by inhalation according to the criteria of Annex VI to Directive 67/548/EEC and in the category 4 according to criteria of CLP Regulation 1272/2008.