Fatty acids, C14-18 and C16-18-unsatd., zinc salts

Short-term toxicity to aquatic invertebrates

Description of key information

Fatty acids, C14-18 and C16-18-unsatd., zinc salts:

Data are not available for the toxicity of Fatty acids, C14-18 and C16-18-unsatd., zinc salts to aquatic invertebrates. Thus, read-across to structural analogue substances, i.e. zinc salts of fatty acids with equal or shorter alkyl chain length [Fatty acids, C16-18, zinc salts; zinc dilaurate (C12)] is applied.

 

The acute toxicity of the structural analogue fatty acids, C16-18, zinc salts to the waterflea Daphnia magna at pH 6 and 8 was not observed at 100 mg fatty acids, C16-18, zinc salts/L resulting in an EC50 > 100 mg/L (Bouwman et al. 2003). Thus, the toxicity to Daphnia magna is above the water solubility limit of around 1 mg/L, and fatty acids, C16-18, zinc salts is not expected to be an acute hazard to aquatic invertebrates. A similar conclusion was made in the 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) as follows: "The acute toxicity of zinc distearate to the waterflea Daphnia magna was determined according to OECD 202 in M7 medium at pH 6 and 8 (see also Chapter 1). Up to a loading rate of 100 mg zinc distearate/L the EC50 was not reached. The zinc concentration (detected using ICP-MS) at the beginning of the test was 1.2 mg Zn/L at pH 8 and 0.8 mg Zn/L at pH 6, at a loading rate of 100 mg zinc distearate/L."Since structural analogues are considered not to be toxic to aquatic invertebrates up to and including the respective water solubility limit of around 1 mg/L, Fatty acids, C14-18 and C16-18-unsatd., zinc salts is also not expected to be an acute hazard to aquatic invertebrates.

The low potential for toxicity is further supported by the results of a screening study on a fatty acid zinc salt of similar chain length, i.e. zinc bis[12-hydroxyoctadecanoate], (Rudolf 2003) in which an EC50 was not reached at a nominal loading of 1000 mg/L (Rudolf 2003). Furthermore, the acute aquatic toxicity of zinc dilaurate (C12) to Daphnia magna is above the water solubility limit of ca. 5 mg/L; an EC50 was also not reached up to 10 mg zinc dilaurate/L at pH 7.8 (Muckle 2009). Thus, acute toxicity data of another structural analogue, i.e. zinc dilaurate - a zinc salt of a shorter-chained fatty acid (C12) with a relatively higher zinc content, support the conclusion that zinc salts of fatty acids are not acutely toxic to invertebrates.

 

Nevertheless, conservative read across to the assessment entities soluble zinc substances and C14-18 fatty acids is applied, since zinc cations and fatty acid anions determine the fate and toxicity in the environment. Since C14-18-satd. and C16-18-unsatd. fatty acids have a low potential for ecotoxicity, the hazard assessment of Fatty acids, C14-18 and C16-18-unsatd, zinc salt is based on zinc ions. Please refer to the endpoint summary of the respective assessment entity for further details.

 

Fatty acid anions (C14-18-satd. and C16-18-unsatd.):

Fatty acids as contained in plant and animal tissue are a natural component of aquatic systems, represent a significant part of the nutritional demands of living organisms, are rapidly degraded and non-bioaccumulative and have a low potential for acute toxicity to aquatic invertebrates.

 

Zinc:

The key data (lowest EC50 values)- all for Ceriodapnia dubia- are summarised as follows:

-at low pH: 0.413 mg Zn/L (single value) and >0.53 mg Zn/L (single value) at low and high hardness, respectively

-at neutral/high pH: 0.147 mg Zn/L (geomean) and 0.228 mg Zn/L (geomean) at low and high hardness, respectively