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

Toxicity to aquatic algae and cyanobacteria

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 freshwater algae and cyanobacteria. 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.

In a growth inhibition test performed according to OECD TG 201, the alga Pseudokirchneriella subcapitata was exposed to dissolved fractions of the structural analogue fatty acids, C16-18, zinc salts at loadings of 0.01, 0.1, 1, 10 and 100 mg/L in standard test medium over a test period of 72 hours (Wenzel, 2013a), the calculated EL10 value for growth rate was 3.31 mg/L (extrapolated) whereas the EL50 is expected to be > 100 mg/L based on loadings of the applied dissolved fraction.

In addition, a growth inhibition test with P. subcapitata exposed to the dissolved fractions of zinc dilaurate at loadings of 0.01, 0.1, 1 and 10 mg/L in standard test medium over a test period of 72 hours revealed calculated EL50 values for growth rate of 12.87 mg/L (extrapolated) while the EL10 was 3.73 mg/L, based on loadings of the applied dissolved fraction (Wenzel, 2013b). In growth inhibition tests of the alga Desmodesmus subspicatus performed with the structural analogue zinc bis[12-hydroxyoctadecanoate] and the shorter-chained zinc dilaurate (C12), 72h-EC50 as well as the 72h-NOEC values far above the maximum water solubility were observed (Rudolph 2002 and Muckle 2009). In sum, zinc salts of fatty acids with a similar structural analogy, water solubility and zinc content are not toxic to algae at concentrations≤relevant acute and chronic aquatic classification criteria; and the potential of Fatty acids, C14-18 and C16-18-unsatd., zinc salts for toxicity to freshwater algae and cyanobacteria is considered similarly low.

 

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, are rapidly degraded and non-bioaccumulative and have of low potential for toxicity to algae.

 

Zinc:

The lowest IC50 amounts to 0.136 mg Zn/L (single value) at neutral/high pH whereas the lowest NOEC is estimated with 0.019 mg Zn/L (geomean of 27 values) - all for Selenastrum capricornutum. Regarding marine algae, NOECs are available for 12 species ranging from 0.0078 to 0.67 mg/L (dissolved concentrations).