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Environmental fate & pathways

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In the assessment of environmental fate of substance Fatty acids, C18-24, zinc salts, read-across to analogue substances and the assessment entities soluble zinc substances and fatty acids is applied since the ions of substance Fatty acids, C18-24, zinc salts determine the environmental fate of substance Fatty acids, C18-24, zinc salts..

Substance Fatty acids, C18-24, zinc salts is produced by the oleochemistry sector, starting from natural fatty materials and consists of approximately 90.5% natural fatty acids and 9.5% zinc. Substance Fatty acids, C18-24, zinc salts is a salt of long-chained fatty acids containing C18-24 C-atoms. Thus, read across of data available for long-chained (C16-18 and 12-HydroxyC18) and shorter-chained (C8) fatty acids based on structural similarity, water solubility and zinc content in a conservative, worst case approach is assumed to adequately describe the biodegradability of substance Fatty acids, C18-24, zinc salts (C18-24).

In the Closed Bottle test according to OECD 301D, 93% of Fatty acids, C16-18, zinc salts was biodegraded after 28 days. This value was calculated from the BOD, the biological oxygen demand, and the ThOD, the theoretical oxygen demand. Fatty acids, C16-18, zinc salts 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. "

A similar zinc salt of a fatty acid (i. e. zinc-12-hydroxystearate) biodegraded up to 71% after 28 days as determined 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.

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 (C8) fatty acid, is readily biodegradable.

Thus, similar biodegradation rates are observed in different tests with zinc salts of short-chained (C8) and long-chained (C16-18) fatty acids.

It is concluded that substance Fatty acids, C18-24, zinc salts is also 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) (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.


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