[No public or meaningful name is available]

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

5 February 2007 to 3 July 2007.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, dried and a ratio of wet to dry weight was calculated. An aliquot of washed sludge was suspended in tap water to obtain a concentration equivalent to 3 g dry material per liter. During the holding period of three days prior to use, the sludge was fed daily with 50 mL synthetic wastewater per liter and was kept at room temperature under continuous aeration until use. Before use, the dry weight of the activated sludge was measured again in the inoculum used for the test. The pH of the activated sludge inoculum was adjusted from 9.0 to 7.0 with a diluted sulphuric acid solution:
16 g peptone
11 g meat extract
3 g urea
0.7 g NaCL
0.4 g CaCL2 . 2H2O
0.2 g MgSO4 . 7H2O
2.8 g K2HPO4

At the start of the test, synthetic wastewater and activated sludge inoculum were added. The inoculum had a sludge concentration of 3.3 g/L dry weight. The sludge was added in time intervals of 15 minutes, first to a control and secondly to the test solutions of the reference item, thirdly to the test suspension of the test item, and finally to the second control.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

24 h

Details on test conditions:

- TEST SYSTEM
Test vessel: closed. 2000 mL glass beakers.
Aeration: during the incubation period of 3 hours, the single test medium and controls were continuously aerated by intense stirring on magnetic stirrers to avoid possible foaming and/or stripping of the test item.
Photoperiod: All test vessels were shielded from the light during mixing.
Temperature: 20°C at the start and the end of the incubation period.

- OTHER TEST CONDITIONS
The pH of the activated sludge inoculum was adjusted from 9.0 to 7.0 with a diluted sulphuric acid solution.

- TEST CONCENTRATIONS
The final nominal concentration tested was 1000 mg/L.

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The test substance had no significant inhibitory effect (15%) on the respiration rate of activated sludge after the incubation period of three hours at the limit test concentration of 1000 mg/L. Based on the physical appearance of the test suspension, the saturation concentration was < 1000 mg/L and resulted in less than 15% inhibition after the three hours of contact time.

Thus the 3-hour NOEC (EC15) of yje test substance to activated sludge microorganisms was at least 1000 mg/L. This value might have been even higher, but concentrations above 1000 mg/L were not tested. The 3-hour EC20, EC50, and EC80 could not be calculated, but were clearly higher than 1000 mg/L.

Results with reference substance (positive control):

Results with reference substance valid? Yes

Validity criteria fulfilled:

yes

Conclusions:

In an OECD 209 study the effect of the test substance on the respiration of activated sewage sludge microorganisms gave a 3-hour NOEC (EC15) of at least 1000 mg/L.

Executive summary:

The inhibitory effect of the test substance on the respiration rate of aerobic
wastewater microorganisms of activated sludge was investigated in a 3-hour respiration inhibition test according to the EU Commission Directive 88/302/EEC, Part C.11, and the OECD Guideline for Testing of Chemicals, No. 209.

In accordance with the EU Commission Directive 92/69/EEC (C.1, C.2, and C.3), a limit test with a nominal test concentration of 1000 mg/L was performed.

In addition, two controls and three different concentrations of the reference item
3,5-dichlorophenol (5, 16, and 50 mg/L) were tested in parallel. The results of these treatments confirmed suitability of the activated sludge and the method used.

The test item had no inhibitory effect on the respiration rate of activated sludge after the incubation period of three hours at the test item concentration of 1000 mg/L. The saturation concentration (water solubility limit of the test substance under the test conditions) was reached and no inhibitory effect was determined after three hours contact time.

Thus, the 3-hour NOEC (EC15) of the test item to activated sludge microorganisms was at least 1000 mg/L. This value might even be higher, but concentrations above 1000 mg/L were not tested. The 3-hour EC20, EC50, and EC80 could not be calculated, but were clearly higher than 1000 mg/L.

Description of key information

In an OECD 209 study the effect of the test substance on the respiration of activated sewage sludge microorganisms gave a 3-hour NOEC (EC15) of at least 1000 mg/L. 

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

The 3-hour NOEC (EC15) of coconut oil reaction products with boric acid and diethanolamine to activated sludge microorganisms was at least 1000 mg/L. This value might have been even higher, but concentrations above 1000 mg/L were not tested. The 3-hour EC20, EC50, and EC80 could not be calculated, but were clearly higher than 1000 mg/L (RCC, 2007).