Zinc dimyristate

Endpoint summary

Description of key information

In the assessment of environmental fate of zinc ditetradecanoate, read-across to analogue substances and the assessment entities soluble zinc substances and tetradecanoic/myristic acid is applied since the ions of zinc ditetradecanoate determine the environmental fate of zinc ditetradecanoate. Zinc ditetradecanoate is produced by the oleochemistry sector, starting from natural fatty materials and consists of approximately 88% natural fatty acids and 13% zinc. It is a zinc salt of a medium-chained fatty acid containing 14 C-atoms. Thus, read-across of data available for zinc salts of shorter-chained (C8 -10) and longer-chained (C16 -18) fatty acids based on structural similarity, water solubility and zinc content in a conservative, worst-case approach is assumed to support conclusions on the biodegradability of zinc ditetradecanoate.

In the static Manometric Respirometry Test (OECD 301 F), the biodegradation of the shorter-chained (C8) octanoic acid, zinc salt, basic (CAS 90480-58-3; consisting of approximately 77% natural fatty acids and 23% zinc) 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, i.e. a zinc salt of a shorter-chained (C8) fatty acid, is readily biodegradable.

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 C18 fatty acid (i.e.Zinc bis[12-hydroxyoctadecanoate], 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 bis[12-hydroxyoctadecanoate]is also readily biodegradable as the 60% level was passed within 28 days but failed the 10-day window criteria.

Thus, similar biodegradation rates are observed in different tests with zinc salts of shorter-chained (C8) and longer-chained (C16-18) fatty acids. Thus, a similar potential for biodegradation may be assumed for zinc ditetradecanoate (C14).

However, only the fatty acid moiety (i.e. octanoate) is biodegradable in the proper sense. Fatty acids, including tetradecanoate, are not persistent in water,and transformation products of environmental concern are also not expected.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 cations, information is available on the removal of zinc from the water column. The removal from the water column was modelled referring to the EUSES model parameters and different conditions of pH. Zinc is removed by > 70% under the reference conditions for the EU regional water (EUSES) (see Mutch Associates, LLC, 2010a,b). Consequently, zinc is considered as equivalent to being ‘rapidly degradable in the context of classification for chronic aquatic effects.

In sum, the moieties of zinc ditetradecanoate are biodegraded or removed from the water column.