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Environmental fate & pathways

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Zinc bis[12-hydroxyoctadecanoate] is produced by the oleochemistry sector, starting from natural fatty materials and consists of approximately 90% natural fatty acids and 10% zinc. Zinc bis[12-hydroxyoctadecanoate] biodegraded up to 71.4% 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 readily biodegradable as the 60% level was passed within 28 days but failed the 10-day window criteria.

Zinc bis[12-hydroxyoctadecanoate] is a zinc salt of a long-chained fatty acid containing 18 C-atoms. Furthermore, data available for zinc salts of fatty acids with a similar chain length (C16- 18) and shorter-chained (C8) fatty acids are read-across as supportive information based on structral similarity, water solubility and zinc content.

In the Closed Bottle test according to OECD 301D, 93% of a structural analogue (i.e. a similar zinc salt of a fatty acid: zinc stearate - fatty acids, C16-18, zinc salts; CAS 91051-01-3) was also biodegraded after 28 days. This value was calculated from the BOD, the biological oxygen demand, and the ThOD, the theoretical oxygen demand. Zinc stearate is readily biodegradable as the 60% level was passed within 28 days but failed the 10 day window criteria. Conclusions from EU RAR Zinc distearate (CAS-No.: 557-05-1 & 91051-01-3 EINECS-No.: 209-151-9 & 293-049-4) Part 1 - Environment (Final report R074_0805_env, May 2008,"Once emitted into the environment, zinc distearate will partly dissociate into the zinc cation and the stearic [CH3(CH2)16COO-] and palmitic [CH3(CH2)14COO-] anions, especially in an acidic environment. The further speciation of zinc, which includes complexation, precipitation and sorption, and the environmental fate of the fatty acids depend on the environmental conditions. In the presence of other cations such as calcium and magnesium, zinc distearate will partly form other “insoluble” stearates (e. g. Schmets, 1996). Stearic and palmitic acid as such are readily biodegradable, although the degradability can be inhibited by the formation of insoluble salts (e. g. calcium, magnesium and zinc distearates), that are not readily biodegradable (BKH, 1994; Schmets, 1996)3. This is confirmed in a OECD 301D study. "

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, i.e. a zinc salt of a shorter-chained (C-8) fatty acid, is also readily biodegradable.

Thus, similar biodegradation rates are observed in different tests with zinc salts of C16 -18-fatty acids as well as zinc salts of

shorter-chained fatty acids. It is concluded that zinc bis[12-hydroxyoctadecanoate] is readily biodegradable.

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. 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 waters (EUSES). Consequently, zinc is considered as equivalent to being ‘rapidly degradable in the context of classification for chronic aquatic effects. For details, please see the Chemical Safety Assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006 in Appendix 1, specifically section 4.6.: "removal from the water" column by Mutch Associates, LLC, 2010 a, b.