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Toxicity to microorganisms

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Description of key information

No toxicity is expected for microorganisms. 

Key value for chemical safety assessment

Additional information

Within the fatty acid category studies describing the toxicity of fatty acids to Pseudomonas putidaare available. For the mixture under discussion two studies were used as read-across from C8 and C12 fatty acids.

For the octanoic acid C8 (CAS 124 -07 -2) and the stearic acid C18 (CAS 57 -11 -4) cell multiplication inhibition tests were conducted following GLP-requirements. The used method in the tests was similar to the ISO guideline 10712. In the study available for octanoic acid an EC10 (18 h) of 912 mg/L (nominal) was reported (Coenen, 1988). Testing of stearic acid resulted in an EC10 (18 h) of 883 mg/L (nominal) (Coenen, 1989). Concluding from the results of both studies both substances are regarded to be not toxic to microorganisms up to their water solubility limit. Octanoic acid (C8) is highly soluble in water (680 mg/L - 789 mg/L). In contrast stearic acid (C18) is nearly insoluble in water (< 0.05 mg/L). Thus as relevant EC10 value for PNEC-calculation 912 mg/L is used.


In addition tests were conducted with the C14 -22 fatty acid mixture (CAS 68424 -37 -3), lauric acid C12 (CAS 143 -07 -7), myristic acid C14 (CAS 544-63-5) and palmitic acid (CAS 57 -10 -3) on Pseudomonas putida according to DIN 38472 Part 27 (Kirch, 1993, Geisel and Berger, 1998 and Kirch 1994 a/b). In these tests EC10 -values of > 3800 mg/L (CAS 71076 -48 -7), >1000 mg/L (CAS 143 -07 -7), >10000 mg/L (CAS 544-63-3) and > 3000 mg/L (CAS 57 -10 -3) were reported after 30 min exposure based on respiration rate. Though these tests do not meet the requirements of todays standard procedures the results are considered reliable to demonstrate the low toxicity of the test substances to microorganisms. Hence, all tests were used for a weight of evidence approach for the fatty acid mixture under discussion here.

Concluding from the available results, fatty acids are regarded as non-toxic to microorganims. For the PNEC-calculation the EC10 -value of 912 mg/L determined for the C8 homologue was used.

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