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Diss Factsheets

Ecotoxicological information

Toxicity to microorganisms

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Link to relevant study record(s)

Description of key information

The lowest EC50-value of 21 mg/L for microorganisms relevant for waste water treatment plants was acquired in a 24 h nitrification test with a nitrifying enrichment culture obtained from the mixed liquor of an activated sludge plant treating meat-packing, rendering, and hide-curing waste-water. 
The toxicity of phenol for Nitrosomonas sp. was tested. The seed bacteria for the nitrifiying enrichment culture were obtained from the mixed liquor of an acitivated sludge plant treating meat-packing, rendering, and hide-curing waste-water. The reactor vessel was a 20 L glass bottle. Diffused aeration provided complete mixing and aeration. The culture was fed two times per day apporximately 1000 mg/L ammonia-nitrogen in an inorganic nutrient solution buffered by sodium bicarbonate. The inhibition of ammonium consumption was used as the criterion for toxic inhibition of Nitrosomonas. Sealed serum bottles (125 mL) were prepared with ammoniua feed and 20 mL of surcharged oxygen. Ammonia was measured at the end of the assay period using an ammonia selective elctrode. Nitrite was checked to ensure that only toxicity to Nitrosomonas and not toxicity to Nitrobacterer was controlling the rate of metabolism activity. A range of toxicant concentrations were tested. Toxicants were tested in at least two experiments. An average IC50 of 21 mg/L was calculated.

Key value for chemical safety assessment

EC50 for microorganisms:
21 mg/L

Additional information

The data on effects of phenol on microorganisms is presented in EU RAR (2006) in Section 3.2.1 (Aquatic compartment (incl. Sediment), at page 42ff). It is stated that as a worst case assumption the EC50 of 21 mg/L (Blum et al., 1991) was used in the risk characterisation for waste water treatment plants.

Results of tests conducted with manifold microorganisms (e.g. waste water sludge, methanogens, activated sludge, several single species) are available. The test methods also vary from short-term tests over 5 min to cell multiplication inhibition test over 48 h. The nitrification (EC50 21 mg/L, Blum et al., 1991) test was selected as key study due to following reasons:

- mixed culture of natural source representative for waste water treatment plants

- sensitive endpoint

- long-term test