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Toxicity to microorganisms

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Reference
Endpoint:
toxicity to microorganisms, other
Remarks:
reduction in the endogenous respiration
Type of information:
experimental study
Adequacy of study:
key study
Study period:
January 2018 - June 2018
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to
Guideline:
other: Good quality data obtained with other types of microbial inhibition test methods, degradation- or sewage treatment simulation tests, can be also used to meet the REACH requirements
Principles of method if other than guideline:
The substance under investigation was evaluated on its inhibition to sludge and river water microorganisms when dosed in the test system in ready biodegradability testing (OECD 301D)
GLP compliance:
no
Analytical monitoring:
yes
Remarks:
Oxygen consuption
Details on sampling:
Monitoring at T 0, 7, 14, 21, 28, 42, 56, 82, 112 and 140 days
Vehicle:
no
Details on test solutions:
Deionized water containing <1.0 mg/L of organic carbon was prepared in a water purification system.

The river water used in the Closed Bottle test was spiked per liter of water with 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.4 mg Na2HPO4·2H2O, 22.5 mg MgSO4·7H2O, 27.5 mg CaCl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was not added to the river water to prevent nitrifi-cation. The test substance (active) and sodium acetate were added to the bottles using aqueous stock solutions of 1.0 g/L.

The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.

The concentrations of the test substance (active) in the bottles was 3.0 mg/L. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Activated sludge was obtained from the wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands. This plant treats predominantly domestic wastewater. The activated sludge was preconditioned to reduce the endogenous respiration rates. To this end, 0.40 g Dry Weight (DW)/L of activated sludge was aerated for one week. The sludge was diluted to 2.0 mg DW/L in the biological oxygen demand (BOD) bottles (Ginkel, van and Stroo, 1992).
River water was sampled from the Rhine near Heveadorp, The Netherlands. The river water was aerated for 7 days to reduce the endogenous respiration. River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating. The river water spiked with mineral salts of the nutrient medium was used undiluted.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
140 d
Remarks on exposure duration:
The inhibition of microorganisms was evaluated based on the endogenous respiration over the first 7 days
Test temperature:
The temperature ranged from 22 to 24°C
pH:
The pH was 7.3 for activated sludge and 8.0 for river water at the start of the test. After 28 days the pH was 7.2 for activated sludge and 7.9 for river water.
Dissolved oxygen:
was monitored
Salinity:
Freshwater
Nominal and measured concentrations:
The concentrations of the test substance (active) in the bottles was 3.0 mg/L.
The ThODNH3 and ThODNO3 used to calculate the biodegradation percentages were 1.15 and 2.30 g O2/g test substance, respectively.
Details on test conditions:
The available result of the closed Bottle test (OECD TG 301 D) is used to evaluate the respiration inhibition of the microorganisms in the inoculum. The closed bottle test has been performed according to slightly modified EU, OECD and ISO Test Guidelines (OECD, 1992; EU, 1992; ISO, 1994) but not in compliance with the OECD principles of Good Laboratory Practice.
Reference substance (positive control):
no
Key result
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
3 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of heterotrophic respiration
Remarks on result:
other: Active ingredient content = 35.8%
Key result
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
0.834 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
inhibition of heterotrophic respiration

Table I Percentages biodegradation of sodium hydrogen substituted amino acid solution (2) in Closed Bottle tests inoculated with activated sludge and river water. The percentages were calculated with the ThODNH3.

Inoculum

Biodegradation percentage at day

7

14

21

28

42

56

84

Sludge

3

5

8

9

24

21

27

River

4

4

0

0

0

7

33

 

Table II Percentages biodegradation of sodium hydrogen substituted amino acid solution (2) in Closed Bottle tests inoculated with activated sludge and river water. The percentages were calculated with the ThODNO3.

Inoculum

Biodegradation percentage at day

7

14

21

28

42

56

84

Sludge

1

3

4

5

12

11

13

River

3

3

0

0

0

4

16

 

Validity criteria fulfilled:
yes
Conclusions:
No respiration inhibition occured to the activated sludge and river water microorganisms present in the inoculum during the first 7 days of a ready biodegradability test at 0.834 mg a.i./L (NOEC = 0.834 mg a.i./L)
Executive summary:

No respiration inhibition occured to the activated sludge and river water microorganisms present in the inoculum during the first 7 days of a ready biodegradability test at 0.834 mg a.i./L (NOEC = 0.834 mg a.i./L)

Description of key information

No respiration inhibition occured to the activated sludge and river water microorganisms present in the inoculum during the first 7 days of a ready biodegradability test at 0.834 mg a.i./L (NOEC = 0.834 mg a.i./L)

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
0.834 mg/L

Additional information

Good quality data obtained with other types of microbial inhibition test methods, degradation- or sewage treatment simulation tests, can be also used to meet the REACH requirements