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Toxicity to microorganisms

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Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
JUSTIFICATION FOR DATA WAIVING
Bis (2-ethylhexyl) adipate (DEHA) is appropriate for read-across because it is considered as a similar substance, based on similar structure, toxicokinetic and toxicological profile useful for this interpolation (please see also read-across justification attached to chapter 13).
Reason / purpose:
read-across source
GLP compliance:
yes
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
> 350 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 350 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Validity criteria fulfilled:
yes
Executive summary:

In an activated sludge respiratory inhibition test according to EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test) with the read-across substance di-2-ethylhexyl adipate as test substance, a NOEC of 350 mg/L was determined. The EC50 was > 350 mg/L. Effect levels are for above the watersolubility of di-2-ethylhexyl adipate.

Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1996
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Version / remarks:
Cited as Directive 87/302/EEC, part C, p. 118 (Biodegradation: Activated sludge respiration inhibition test)
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: The test substance were added directly into the test vessels.
Test organisms (species):
activated sludge
Details on inoculum:
- Laboratory culture: obtained from municipal wastewater treatment plant of Marl-Ost (Germany), which predominantely treats domestic sewage.
- Preparation of inoculum for exposure: The activated sludge were centrifuged four times for 5 min at 2000 rpm and cleaned afterwards with 600 mL tap water.
- Initial biomass concentration: 3.7 g suspended solids/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
18 - 20.6 °C
pH:
7.8 - 8.4
Nominal and measured concentrations:
Nominal: 100.8, 127.4, 190.8, 269.6 and 352.4 mg/L
Details on test conditions:
TEST SYSTEM
- Aeration: continuously
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap water
- Intervals of water quality measurement: at the end of the incubation phase (after 3h)

EFFECT PARAMETERS MEASURED: O2 consumption was measured for 8 minutes after an incubation time of 3h.
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
> 350 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 350 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3h) = 5.5 mg/L

Table 1: Respiration inhibition of control, test and reference substance

 Treatment

Nominal concentration [mg/L]

Measuring time

Inhibition [%]

Test item

352.4

5

-6.6

Test item

269.6

6

-8.0

Test item

190.8

6

-6.6

Test item

127.4

6.5

-7.7

Test item

100.8

5

-9.7

Reference

5

6.5

45.9

Reference

15

7.5

77.9

Reference

30

8

86.1

Control

 

6.5

 

Control

 

7

 

Validity criteria fulfilled:
yes
Conclusions:
A 3h respiration inhibition test with domestic activated sludge revealed that DEHA is not inhibitory to aquatic microorganisms up to the saturation limit in water.
Executive summary:

A 3h activated sludge respiration inhibition test was performed according to EU method C.11 under GLP conditions. Different test concentrations up to ~ 350 mg/L were tested. No respiration inhibition but stimulation was observed in all treatments compared to the control. Thus, the 3h-EC50 value is determined to be above the highest concentration tested : >350 mg/L.

Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when the test substance is introduced in appropriate low concentrations.

Key value for chemical safety assessment

Additional information

In an activated sludge respiratory inhibition test according to EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test) with bis(2-ethylhexyl) adipate as test substance, a NOEC of 350 mg/L was determined. The EC50 was > 350 mg/L. Effect levels are for above the limit of water solubility of bis(2-ethylhexyl) adipate.