Difluoromethane

Toxicity to aquatic algae and cyanobacteria

Description of key information

The 96-h EC50 for algae estimated using ECOSAR v1.11 for neutral organics is 313 mg/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 EC50 (96h) = 313 mg/l and this result is used in the assessment.  

In a supporting read-across study with the analogue substance HFC-245fa, slight growth inhibition was observed at 118 mg/l test substance. The 72 hour EC50 was greater than 118 mg/l. In a second supporting read-across study with the analogue substance HFC-365mfc, no EC50 for biomass and growth rate could be determined at any timepoint (72h-EC50 > 114 mg/l). A 72h-NOEC of 13.2 mg/l was determined both for biomass and growth rate. Both studies support the fact that substances in this category are not likely to be toxic to algae, even when volatilization is minimized.

Key value for chemical safety assessment

EC50 for freshwater algae:

313 mg/L