Difluoromethane

Short-term toxicity to fish

Description of key information

The 96-h LC50 for freshwater fish estimated using ECOSAR v1.11 for neutral organics is 1731mg/l.

Given the physical nature of difluoromethane and due to the difficulty to test it meaningfully, no experimental aquatic results are available. Instead, QSAR methods were used to estimate the toxicity of the substance to aquatic organisms. The effect concentrations of difluoromethane were estimated using the method described in the EU Technical Guidance Document (2003) and/or the US EPA program ECOSAR (v1.11, 2012). The measured log Kow value of 0.21 was used for the predictions using both QSARs.

Only calculated effect concentrations are available, all calculations are reliable and the substance properties fall within the applicability domain of the QSARs as described in the QPRF report attached. The calculated acute effect parameter using ECOSAR v1.11 resulted in an LC50 (96h) = 1731 mg/l and this result is used in the assessment.  

In a supporting read-across study with the analogue substance HFC-245fa, no fish mortality was observed at a nominal concentration of 100 mg/l (mean measured concentration 81.8 mg/l). The study design was developed to minimize volatilization and obtain the maximum attainable concentration. Therefore, although the LC50 could not be identified, it must be > 100 mg/l. Three fish exhibited darkened pigmentation during the limit test. This study supports the fact that substances in this category are not likely to be toxic to fish, even when volatilization is minimized.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

1 731 mg/L