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Toxicity to microorganisms

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Toxicity to microorganisms: Weight of evidence: Experimental results obtained with the substance trichloroacetic acid and read-across from the results obtained with sodium trichloroacetate. 

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Toxicity to microorganisms: Weight of evidence: Experimental results obtained with the substance trichloroacetic acid and read-across from the results obtained with sodium trichloroacetate.

Trichloroacetic acid:

In an activated sludge respiration inhibition test, conducted with industrial activated sludge exposed to the substance trichloroacetic acid, the 24 -h EC20 was higher than 750 mg/l.

The luminiscent bacteria toxicity (LBT) test was performed on the marine phosphorescent bacterium Photobacterium phosphoreum. This test was conducted using the Microtox Toxicity Analyzer System. The EC50 for trichloroacetic acid in the LBT test was 35 mg/l. Single species test with Photobacterium phosphoreum (Vibrio fischeri) should be considered of low relevance for STPs (Sewage Treatment Plants).

Sodium trichloroacetate:

Free trichloroacetic acid is a strong organic acid, which forms water-soluble salts with bases. In any medium at or near neutral pH the predominant form present is the trichloroacetate anion. The salts are therefore expected to be toxicologically equivalet to the free acid, except for the acute corrosive properties, which are at least partly determined by the very low pH of strong solutions of the acid. Using analogous methods of the cell multiplication inhibition test, the toxicity threshold (TT) of sodium trichloroacetate was determined for model organisms. The toxicity threshold was greater than 1000 mg/l for the bacteria Pseudomonas putida and 800 mg/l for the protozoan species Entosiphon sulcatum.

The assimilation-depletion test (A-D test) was performed. The oxygen consumption of a natural bacterial population (depletion test) serves as measurement criteria. The 24 -h EC10 for sodium trichloroacetate for a mixture culture of heterotrophic bacteria was greater than 1000 mg/l.

A method of testing the toxicity of sodium trichloroacetate to bacterial organisms was performed at concentrations ranging from 10 to 1000 mg/l. After incubation of 24 hours at 30 ºC, the measurement of bacterial toxicity was carried out by determining the minimum inhibitory concentration (MIC) in mg/l of the test substance. The MIC was 1000 mg/l for the tested species Aeromonas hydrophila and Bacillus subtilis.

Based on the results obtained with the substance sodium trichloroacetate and applying the read-across approach taking into account the molecular weights of the substances, it is concluded that for the substance trichloroacetic acid, the toxicity threshold for the species Pseudomonas putida and the 24 -h EC10 for a mixture culture of heterotrophic bacteria would be greater than 880 mg/l. The MIC for the species Aeromonas hydrophila and Bacillus subtilis would be 880 mg/l.