Plastic, waste, pyrolized, fractionation bottoms

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

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))

GLP compliance:

yes

Hardness:

All chemicals used in the test were “analytical grade” or “for use in microbiology”.
Composition of nutrient solution (synthetic sewage):
Peptone 16.0 g
Meat Extract 11.0 g
Urea 3.0 g
NaCl 0.7 g
CaCl2*2H2O 0.4 g
MgSO4*7H2O 0.2 g
K2HPO4 2.8 g
Deionised water ad 1000 mL

Test temperature:

room temperature

pH:

The pH of the solutions was 7.0, and therefore within the range of 7.5 ± 0.5.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol (1,3-Dichloro-5-hydroxybenzene, C6H4Cl2O, CAS-No. 591-35-5) was used as positive control. A stock solution in deionised water containing 501 mg/L (first and third experiment) was freshly prepared for each experiment.

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

ca. 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 3 200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Results with reference substance (positive control):

The blank controls oxygen uptake rate should not be less than 20 mg oxygen per gram of activated sludge (dry weight of suspended solids) in 1 hour.
Table 8.3-a Oxygen Uptake Rate Date of Experiment Oxygen Uptake Rate in mg/h per gram activated sludge
29. Apr. 2021
20.76 mg oxygen per gram sludge in 1 hour
02. Jun. 2021
27.94 mg oxygen per gram sludge in 1 hour

Validity criteria fulfilled:

yes

Conclusions:

3h NOEC = 100 mg/L
3h EC10 is not determinable
3h EC50 > 3200 mg/L

Executive summary:

Three experiments were performed.
In the second experiment (first main test) one of the validity criteria was not met (the oxygen uptake rate in the blank controls was less than 20 mg O2/h/g sludge). Therefore, the study was repeated. The results of the second experiment (first main test) are not stated in the report, but will be kept together with the other raw data in the GLP archive of the test facility.
In the first experiment (pre-test) the test item was tested using 4 concentrations ranging from 1000 to 1 mg/L nominal concentration. Duration of the test was 3 hours. Activated sludge was used as inoculum. It was taken from a domestic sewage treatment plant and washed before usage. The dry matter was determined as 2.58 g suspended solids/L, giving a con-centration of 1.29 g suspended solids/L in the test.
3,5-Dichlorophenol was used as positive control. Four concentrations were tested; an EC50 of 6.6 mg/L (95% confidence interval: not determinable) was determined, which lies within the recommended range of 2 – 25 mg/L, as stated in the OECD guideline.
Because significant inhibition was observed, one additional experiment was performed un-der the same test conditions.
In the third experiment (second main test) the test item was tested using 5 concentrations ranging from 3200 to 32 mg/L nominal concentration.
The dry matter of the inoculum was determined as 2.58 g suspended solids/L, giving a con-centration of 1.29 g suspended solids/L in the test.
For the positive control an EC50 of 13 mg/L (95% confidence interval: not determinable) was determined. The value lies within the recommended range of the OECD guideline.
The coefficient of variation of oxygen uptake rate in control replicates was below 30% at the end of the test. The oxygen uptake rate of the blank controls was above 20 mg O2 per gram activated sludge in one hour.
Inhibition at the highest concentration 3200 mg/L did not reach 50 % in none of the 5 repli-cates which were tested. Therefore, the EC 50 was stated as > 3200 mg/L. However, due to the test item properties (poorly soluble and therefore poorly bioavailable), the inhibition values within the 5 test replicates for all concentrates were sometimes highly scattered and no clear dose-response relationship was observed. Therefore, no graphical determination of an EC 10 via a regression analysis was possible.
For determination the NOEC, the mean O2 consumption of the test replicates at the concen-tration 100 mg/L was compared with the mean O2 consumption of the control replicates. No significant difference was observed between the concentration 100 mg/L and the control. The NOEC is therefore stated as 100 mg/L.
No observations were made which might cause doubts concerning the validity of the study outcome.

Key value for chemical safety assessment

EC50 for microorganisms:

3 500 mg/L