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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

EC50-3h was determined to be higher than 1000 mg/L. 

Key value for chemical safety assessment

Additional information

The toxicity of 1,2,4 triazole was studied according to an OECD 209 guideline and GLP requirements (Muckle, 2009). All validity criteria were met.

The inhibition which was caused by the test item1,2,4-Triazole did not rise above 45%. The graph inhibition vs. concentration shows a very gentle slope altogether. No adequate increase in inhibition was observed. In the first experiment, 27% inhibition (mean) was observed at the lowest concentration of 1 mg/L. The inoculum in the first experiment was more sensitive than in the second experiment. Therefore, the inhibition values in the second experiment (test item and positive control) were slightly lower. But the difference within the values was in a normal range of a biological system.

Due to the test item’s properties (inhibitor of nitrification), the test item shows stronger inhibitory action to nitrifying micro-organisms which are present in the activated sludge, so that respiration of these micro-organisms is completely inhibited, whereas carbon oxidising micro-organisms are less inhibited. So in an additional experiment in presence of an inhibitor in all treatments (control, positive control and test vessels), calculation of the separate total, heterotrophic and nitrification oxygen uptake rate would have been possible. But in the highest concentrated treatment low total inhibition values (< 50%) were found; the calculated EC50 for total respiration is above 1000 mg/L. Therefore, the sponsor decided that no second experiment had to be performed in order to discern between inhibition of nitrificators and inhibition of total population.

The result of the test can be considered valid.