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Toxicity to aquatic algae and cyanobacteria

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Description of key information

PFPA (degradation product) CAS# 422.64-0: Pseudokirchneriella subcapitata 72-hour EC50, 10.6 mg/L; 96-hour NOEC, 3.71 mg/L (OECD TG201).

Key value for chemical safety assessment

Additional information

Toxicity of CAS# 756-13-8 to freshwater algae was addressed in studies using either the substance itself or perfluoropropionic acid (PFPA, CAS# 422-64-0).  When CAS# 756-13-8 is tested directly (at nominal concentrations), measured concentrations of PFPA are included in the study reports. CAS# 756-13-8 hydrolyzes completely with a half-life < 2.5 minutes when forced into contact with water to PFPA and a volatile hydrofluorocarbon (heptafluoropropane).  Therefore, toxicity tests based on measured PFPA concentrations provide a more realistic appraisal of the effects of the test substance in the aquatic environment.

 

All studies were performed in accord with established test guidelines and were in compliance with OECD GLP standards.  Cell concentrations were determined daily by direct haemocytometer counts.  In addition, relative size differences, unusual cell shapes, colors, flocculations, adherence of cells to test containers, or aggregation of cells were assessed.  In the first key study, PFPA was used as the test substance.  The Pseudokirchneriella subcapitata 72-hour EC50 was 10.4 mg/L PFPA, the 96-hour EC50 was 10.6 mg/L PFPA, and the 96-hour NOEC was 3.71 mg/L PFPA.  Although the second key study and all supporting studies were executed using CAS# 756-13-8 at nominal concentrations, all toxicity endpoints are evaluated with respect to measured concentrations of PFPA to facilitate comparison. In the second key study, the Pseudokirchneriella subcapitata 72-hour EC50 was > 6.8 mg/L, the 96-hour EC50 was > 6.8 mg/L, and the 96-hour NOEC was 3.47 mg/L.  In the first supporting study, the Navicula pelliculosa 72-hour EC50 was > 14.2 mg/L, the 96-hour EC50 was > 14.2 mg/L, and the 96-hour NOEC was 14.2 mg/L.  In the second supporting study, the Anabaena flos-aquae 72-hour EC50 was > 86.6 mg/L, the 96-hour EC50 was > 86.6 mg/L, and the 96-hour NOEC was 44.0 mg/L.  The results indicate that Pseudokirchneriella subcapitata is the most sensitive of the three species tested to PFPA-induced toxicity.  With the assumption of no loss to volatilization, the 72-hour EC50 in the key study is equivalent to 20.0 mg/L CAS# 756-13-8, the 96-hour to 20.4 mg/L CAS# 756-13-8, and the 96-hour NOEC to 7.15 mg/L of CAS# 756-13-8.  Based on the results of the key study, both CAS# 756-13-8 and PFPA are classified as Acute 3 to algae in accordance with the classification system of the Globally Harmonized System (GHS).

 

All studies were performed according to accepted international guidelines for testing of chemical toxicity to algae and cyanobacteria and are thus relevant to this endpoint.  The key study was performed in accord with OECD TG201 (7 June 1984) and OPPTS 850.5400 (public draft, Apr. 1996), and was in compliance with OECD GLP standard C(97)186/Final (1997) and US EPA GLP standards in 40CFR792 (1993). The key study is classified as acceptable and satisfies the guideline requirements for test method OECD TG201 (Alga, Growth Inhibition Test).  The supporting studies were performed in accord with OECD TG201 (7 June 1984) and were in compliance with OECD regulation C(97)186/Final (1997).   Supporting studies one and two are also classified as acceptable and satisfy the guideline requirements for test method OECD TG201.  Supporting study three is classified as unacceptable.  Control vessels did not meet the validity criterion that variance in section-specific growth rate variance must be less than 35%.  This is likely due to the difficulty typically encountered with counting Anabaena cells.  Nevertheless, based on results of the range-finding and definitive studies the reported endpoints are believed to be reasonable estimates of the NOEC and EC50, and the results of this study are consistent with the key study result.  The two studies involving Pseudokirchneriella subcapitata provide very similar estimates of NOEC (3.71 v. 3.47), although the EC50 exceeds the highest concentration tested in the supporting study.  The remaining supporting studies indicate that Pseudokirchneriella subcapitata is the most sensitive of the species tested, and that this species provides a conservative estimate of PFPA toxicity to algae and cyanobacteria.