Difluoromethane

Endpoint summary

Description of key information

Acute inhalation toxicity of difluoromethane is very low with no mortality or other significant effects in rats after 4 hours exposure up to 520000 ppm (1107000 mg/m3).

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP compliant, near guideline study, available as unpublished report, no restrictions, fully adequate for assessment (SIDS score: 1).

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

GLP compliance:

yes

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

other: Wistar-derived

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Olac Limited, Blackthorn, Bicester, Oxon, UK.
- Age at study initiation: young adults
- Weight at study initiation: 264-313 g (males) and 206-251 g (females)
- Housing: 5 per cage (sexes separately)
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: not specified

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 15-24
- Humidity (%): 50+/-15
- Air changes (per hr): 20-30
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: gas

Type of inhalation exposure:

nose only

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure generation: The test atmosphere was generated by passing HFC 32 from the stoch cylinder through a copper coil (4 mm id, length approximately 3-4 m) immersed in a water bath maintained at 40°C. The resulting gas was metered at a flow rate of 2.5 l/min into a monitored airstream (mixture of nitrogen and oxygen at a combined flow rate of 2.5 l/min) and into the bottom level of a PERSPEX Serial Dilution Exposure Chamber. At successively higher levels in the chamber, the atmosphere was further diluted by the addition of clean, dry air (dried and filtered using equipment supplied by Atlas-Copco, Sweden) and the removal of atmosphere via a vacuum line. Air flow rates were measured using variable area flowmeters, recorded at frequent intervals and were altered as necessary to maintain the target concentrations.
- Exposure chamber volume: length 37 cm, width 33 cm, height 20 cm
- Method of holding animals in test chamber: restraining tubes supplied by Battelle
- Method of conditioning air: mixture of nitrogen and oxygen, at successively higher levels further diluted by addition of clean, dry air
- Temperature, humidity in air chamber: 20.5-21.4°C, 39-55%

TEST ATMOSPHERE
- Brief description of analytical method used: By sampling the test atmosphere using a gas tight syringe. The samples were injected on to a gas chromatograph equipped with a flame ionisation detector.
- Nominal/analytical concentrations (NC/AC): The nominal atmospheric concentration is a concentration based on the known flow rates of test material and dilution air during the exposure period. This represents the maximum concentration to which the animals could be exposed assuming no losses within the generation or exposure systems. The nominal concentration of the test material during the exposure generation period was calculated from the following formula: NC = (FR1 / FR1 + FR2) x NC1 where FR1 and FR2 are the flow rates (l/min) of atmosphere from previous level and of dilution air respectively, NC1 is the nominal concentration of previous level.
For the highest exposure level (first stage in the dilution chamber), the nominal concentration of the previous level is 10E6ppm (ie the neat test material). To maintain an oxygen content of 20-21%, an "artificial" atmosphere was generated using a mixture of oxygen and nitrogen added to the stream of HFC32.

Analytical verification of test atmosphere concentrations:

yes

Remarks:

Concentrations monitoring: every 20 minutes samples were taken during each exposure and were analysed by gas chromatography (Chromatograph: Pye Unicam Series 204, Column: Porapak PS. (80/100 Mesh) 1.5 m x 2 mm I.D., flame ionisation detector)

Duration of exposure:

4 h

Concentrations:

Nominal and analytical concentrations are as follows (NC/AC): 17280/7510 ± 4700, 10800/85900 ± 29400 and 500000/520000 ±19200 ppm.

No. of animals per sex per dose:

5

Control animals:

yes

Details on study design:

Duration of observation: 14 days
- Clinical signs: examined once daily
- Mortality: recorded once daily
- Body weight: measured on days 1, 2, 3, 8 and 15.
- Necropsy:
macroscopic examination of the main organs with particular attention to abdominal and thoracic viscera.
lungs (with trachea and larynx attached) were weighed.
microscopic examination: lungs (with bronchi) and any abnormal tissue were fixed with 10% neutral buffered formaldehyde for possible examination.

Statistics:

two-sided Student's t-test

Key result

Sex:

male/female

Dose descriptor:

LC0

Effect level:

> 520 000 ppm

Based on:

test mat.

Exp. duration:

4 h

Mortality:

No deaths occurred during the study.

Clinical signs:

other: - During exposure: Treatment-related findings seen during exposure were confined to animals exposed to 85900 or 520000 ppm HFC 32 and these included auditory hypoaesthesia (in both groups) and increased breathing depth and reduced breathing rate in anima

Body weight:

There were no toxicologically significant effects on bodyweights of treated animals when compared to controls.

Gross pathology:

There were neither significant effects on absolute or relative lung weights nor gross findings at necropsy which were considered to be related to treatment.

Interpretation of results:

practically nontoxic

Remarks:

Migrated information

Conclusions:

Nose-only exposure for 4 hours to analysed atmospheric concentrations of 7510, 85900 or 520000 ppm v/v HFC 32 resulted in no mortalities and no severe toxicity. It is concluded that the median lethal concentration of HFC 32 in the rat exceeds 520000 ppm.

Executive summary:

In an OECD guideline study (Parr-Dobrzanski RJ et al., 1992), 10 Wistar rats (5 males and 5 females) were exposed until 520,000 ppm (1,107,000 mg/m3) of difluoromethane (HFC-32) in atmosphere for 4 hours. The acute inhalation toxicity of difluoromethane was very low with no mortality. Minor clinical signs were observed in the animals exposed to the two highest concentrations (85900 ppm (183,000 g/m3) and 520000 ppm (1,107,000 g/m3) during and after exposure: reduced breathing rate, reduced activity, salivation, tail erections. Affected animals showed a rapid reversal of effects after the end of exposure.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

1 107 000 mg/m³ air

Quality of whole database:

Good with a reliable study.

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In accordance with section 2 of REACH Annex XI, an acute oral and an acute dermal toxicity study do not need to be conducted as the substance is a gas.

The acute inhalation toxicity of difluoromethane is very low with no mortality in rats after 4 hours exposure to atmospheric concentrations of 7510, 85900 or 520000 ppm. Minor clinical signs were observed in the animals exposed to the two highest concentrations (85900 ppm (183000 mg/m³) and 520000 ppm (1107000 mg/m³)) during and after exposure: reduced breathing rate, reduced activity, salivation, tail erections. Affected animals showed a rapid reversal of effects after the end of exposure.

Justification for classification or non-classification

No mortality or other major significant effects occurred after exposure to 520000 ppm (1107000 mg/m³) difluoromethane for 4 hours. Therefore, the substance does not need to be classified for acute toxicity according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.