Octanoic acid, zinc salt, basic

Endpoint summary

Description of key information

Octanoic acid, zinc salt, basic is biodegradable:

Octanoic acid, zinc salt, basic (CAS 90480-58-3) is produced by the oleochemistry sector, starting from natural fatty materials and consists of a maximum of 78 % natural fatty acids and 24% zinc. It is a zinc salt of a shorter-chained fatty acid containing 8 C-atoms.

In the static Manometric Respirometry Test (OECD 301 F), the biodegradation of octanoic acid, zinc salt, basic (CAS 90480-58-3) after 28 days was 80% and 86% at 30 mg/L and 100 mg/L, respectively, meeting the 10-day window criteria. Thus, octanoic acid, zinc salt, basic, is readily biodegradable.

Similar biodegradation rates are observed in different tests with zinc salts of longer-chained (C16 -18) fatty acids: In the Closed Bottle test according to OECD 301D, 93% of zinc stearate (i.e. Fatty acids, C16 -18, zinc salts; CAS 91051-01-3) was biodegraded after 28 days. Zinc stearate is readily biodegradable as the 60% level was passed within 28 days but failed the 10 day window criteria. Another zinc salt of a C-18 fatty acid (i.e. zinc-12-hydroxystearate, CAS 35674 -68 -1) biodegraded up to 71% after 28 days in the OECD 301B test with 14.5 % after 4 days and 53.5% after 13 days. Zinc-12-hydroxystearate is also readily biodegradable as the 60% level was passed within 28 days but failed the 10-day window criteria.

 

 

However, only the fatty acid moiety is biodegradable in the proper sense. The concept of “biodegradability” has been developed for organic substances and is not applicable to inorganic substances, including zinc. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” has been developed to assess whether or not a respective metal ion would remain present in the water column upon addition (and thus be able to exert a chronic effect) or would be rapidly removed from the water column. In this concept, “rapid removal” (defined as >70% removal within 28 days) can be considered equivalent to “rapid degradation”. For zinc in water, information is available on the removal of zinc from the water column (IUCLID section 5.6.). The removal from the water column was modeled referring to the EUSES model parameters and different conditions of pH. Zinc is removed by > 70% under the reference conditions for the EU regional waters (EUSES) (see section 5.6.: "removal from the water" column by Mutch Associates, LLC, 2010a,b). Consequently, zinc is considered as equivalent to being ‘rapidly degradable in the context of classification for chronic aquatic effects.