Formic acid

Toxicity to microorganisms

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

72 mg/L

Additional information

As key study regarding toxicity to microorganisms, an inhibition control of a test on ready biodegradability according to EU method C.3 was identified, using domestic activated sludge as inoculum. Within the test period of 13 days, no inhibition of degradation activity could be observed. Hence, the test substance concentration of 72 mg/L is considered to be a NOEC, used for PNEC derivation.

Furthermore, three relevant and reliable supporting studies are available. One is a respiration inhibition test with industrial activated sludge following ISO/DIS 8192 Part B (draft 1984) which is similar to OECD TG 209 (BASF AG, 1988). Although performed under non-neutralized conditions, stimulation rather than an inhibition of the respiration activity was measured at a test concentration of 988 mg formic acid/L. Therefore, the EC₂₀ was > 988 mg/L.

The second and third study is a growth inhibition test with Pseudomonas putida following the German Industrial Standard DIN 38412, part 8 (BASF AG, 1991; Trenel et al. 1982). The EC₅₀was determined to be 46.7 mg formic acid/L in the test performed by BASF while Trenel et al. found an EC10 of 3160 mg/L. Besides the fact that the result of the BASF study is driven by the acidity of non-neutralized formic acid and that the documentation of the study of Trenel et al. does not contain information on pH value while testing , this type of study using Pseudomonas putida is less relevant for this endpoint since glucose was added as substrate (rf. REACh Guidance r10 and TGD, 2003).

As all supporting studies reveal methodological deficiencies (industrial sludge used; pH dependent effect; no details on test performance), the inhibition control of the biodegradability test was chosen to be the key study.