Pentafluoroethane

Toxicity to aquatic algae and cyanobacteria

Description of key information

Based on available data on structural analogs

Key value for chemical safety assessment

EC50 for freshwater algae:

114 mg/L

Additional information

The assessment of the possible aquatic toxicity of HFC 125 has been carried out by considering available data on structurally analogue substances.

Experimental data for acute toxicity on Selenastrum capricornutum are available for HFC 245fa (1,1,1,3,3-pentafluoropropane) and HFC 365mfc (1,1,1,2,2 -pentafluorobutane). Moreover, the QSAR estimation performed for HFC 32 (difluoromethane) has been used to add further weight in the evaluation.

The experimental studies were conducted in closed systems to avoid substance volatilisation.

In all cases, results indicate a low toxicity to algae. The QSAR estimation for HFC 32 estimated a 72 hour-EC50 of 142 mg/l, whereas no EC50 was identified in the studies for HFC 245fa and HFC 365mfc, as low toxicity was observed up to the highest tested concentrations. Overall, a 72 hour-EC50 = 114 mg/l (i.e. the lowest value determined for structural analogs) can be considered a conservative estimation for HFC 125.

HFC 245fa: The toxicity of pentafluorobutane to S. capricornutum was studied in a test carried out in accordance to OECD guidelines. A closed system was used in order to limit the substance volatility. The substance was tested at the nominal concentration of 100 mg/l (measured concentrations = 108 mg/l and 128 mg/l at 0 and 72 hours, respectively). Inhibition of 7 % and 22 % were observed at the end of the study for biomass and growth rate, respectively. No EC50 could be determined (72 hour-EC50> 118 mg/l average concentration).

HFC365mfc: The toxicity of pentafluorobutane to S. capricornutum was studied in a test carried out in accordance to OECD guidelines. A closed system was used in order to limit the substance volatility. The algae medium was adapted to the close system conditions by adding a higher concentration of NaHCO3, in order to maintain a sufficient dissolved CO2 concentration. Pentafluorobutane was tested at nominal concentrations of 0, 3, 10, 30, 100 and 300 mg/l (mean measured concentrations: 0, 2.0, 4.8, 13.2, 45.6 and 114 mg/l). Algae were exposed for 3 days to the substance and the cell densities were measured at the end of the testing period via spectrophotometric analysis. The biomass integral and the growth rate were calculated from the cell density determinations. All the test acceptability criteria were met.

Pentafluorobutane showed a low toxicity to algae: no EC50 for biomass and growth rate could be determined at any timepoint (72h-EC50 > 114 mg/l). A 0 -72 h NOEC of 13.2 mg/l was determined both for biomass and growth rate.

HFC 32: The 96-h EC50 for algae estimated using ECOSAR v1.00 for neutral organics is 142 mg/l. The calculation is reliable, validated and substance properties fall within the applicability domain of the QSAR.