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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

CAS# 756-13-8 cannot be meaningfully examined in biodegradation assays due to rapid hydrolysis.
PFPA (degradation product), CAS# 422-64-0, is not readily biodegradable; 1.8-3.4% (CO2) in 28 days (OECD 301B)

Key value for chemical safety assessment

Additional information

PFPA is the hydrolysis product of CAS# 756-13-8.  Although CAS# 756-13-8 is immisible with water, it hydrolyzes completely when forced into contact with water to PFPA and a volatile hydrofluorocarbon (heptafluoropropane), with a half-life of <2.5 minutes.  Therefore, biodegradation testing of PFPA provides a more realistic appraisal of this endpoint than testing of CAS# 756-13-8 itself.  The ready biodegradability of PFPA was examined in two studies performed in accord with OECD guidelines and compliant with OECD principles of Good Laboratory Practice.  In the key study, PFPA showed 1.8-3.4% biodegradability (CO2) after 28 days but did not inhibit the microorganisms in the toxicity control.  In the supporting study, PFPA showed 0-2% biodegradability after 28 days, with results dependent upon analytical method.  Thus, the test substance is classified as not readily biodegradable, and the lack of biodegradability is not due to inhibition of degrading microorganisms.  This is the expected result and is in agreement with the extreme stability of the carbon-fluorine bond. 

 

Both studies cite internationally accepted test guidelines for biodegradation in water: screening studies and are therefore intrinsically relevant to this endpoint.  The key study was performed in accord with OECD TG301B (1992) and U.S. EPA (TSCA) Guideline 796.3260 (1993), and in compliance with OECD regulation C(97) 186/Final (1997).  The key study is classified as acceptable and satisfies the guideline requirements for a modified Sturm ready biodegradability test.  The supporting study was apparently conducted in accord with OECD TG301C (17 July, 1992) and in compliance with OECD principles of Good Laboratory Practice (26 November, 1997).   However, the supporting study report was available only in Japanese with a brief synopsis, a small number of phrases, and some data tables and figures in English.  While the result of the supporting study is consistent with the key study, the reliability of the supporting study cannot be addressed.