Barium 4-dodecylphenolate

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:

20-09-2019 till 22-11-2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2019-09-16

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Preparation of stock solution and test solutions:
- A stock solution was prepared by dissolving 4.1298 g of the test item in 2000 mL of deionised water (nominal concentration 2.065 g/L). The stock solution was stirred on a magnetic stirring device until each single test vessel was prepared.
- The test item concentration levels were prepared by combining 16 ml of synthetic sewage feed with corresponding amounts of temperature adapted deionised water and/or stock solution in a way that a volume of 300 ml was obtained. Afterwards 200 ml of the microbial inoculum were added.
- The controls were prepared by combining 16 ml of the synthetic sewage feed with 284 ml of temperature adapted deionised water and adding 200 ml of the microbial inoculum.
- The total mixture volume for each of the test item concentrations and the controls was 500 mL per vessel. Immediately after preparation the test solutions were aerated.
- The test vessels were prepared at intervals of 15 minutes, starting with the first control, followed by the test item concentration levels. Replicates C6B (highest concentration level) and C0B (second control replicate exposed at the end of the testing series) were prepared 17 minutes after the preceding vessel to ensure equal exposure periods (3 hours) and maximum measurement periods (up to 10 minutes) for all vessels when testing the increased number of 14 test vessels.
- At the end of the contact time (test period), the content of the first test vessel (control 1) was poured into the measuring apparatus (consisting of oxygen-meter, flat bottom flask and stirring device) and the respiration rate was determined at two-second intervals over a period of up to 10 minutes. All other test vessels were measured according to this procedure in the same order which was established for the preparation of the test vessels.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge from a sewage treatment plant was used as the microbial inoculum for the test. The activated sludge was obtained from the sewage treatment works in Siddaganaga Institute of Technology, Tumkur treating predominantly domestic sewage.
- Washing medium for activated sludge: deionised water
- Frequency of washing: two times; between washings the activated sludge was centrifuged for 10 minutes at 10,000 m/s2

Pretreatment:
The sludge was collected and coarse particles were removed by settling for a short period, for about 15 minutes, and decanting the upper layer of finer solids. The suspended solids concentrations of the activated sludge were prepared for about 2 g/L to 4 g/L in a bulk quantity.
Sludge solid concentration: 3 g/L.
The activated sludge was continuously aerated at the test temperature (20 ± 2°C) until use.

Synthetic Sewage Feed Medium:
- Peptone: 16.0
- Meat extract: 11.0
- Urea: 3.0
- NaCl: 0.7
- CaCl2 * 2 H2O: 0.4
- MgSO4 * 7 H2O: 0.2
- K2HPO4: 2.8

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20 ± 2°C

pH:

7.5 ± 0.5°C

Dissolved oxygen:

60-70% saturation

Nominal and measured concentrations:

nominal test item concentrations: 131.89 mg/L, 234.76 mg/L, 417.88 mg/L, 743.82 mg/L, and 1324 mg/L (dry mass of barium content) based on the geometric spacing factor 1.78

Details on test conditions:

- Storage time of the activated sludge before use:
- Test vessels: 1000 mL glass beakers
- Amount of test mixture per test vessel: 500 mL
The dry mass of a known volume of the stock suspended solids concentration was determined and the sludge was diluted further in

- Number of test concentrations: 5 plus control
- Number of replicates per test item concentration: 5
- Number of replicates in the control: 6
- Aeration of test vessels: 0.6 L/min

An oximeter HQ40D Multimeter (HACH/HQ40D) was used to determine the oxygen content of the test solutions. After three hours of incubation (contact time), samples were withdrawn to measure the rate of decrease of the concentration of dissolved oxygen in the measuring cell. The cell was rinsed with water between the measurements. The concentration of dissolved oxygen was measured and recorded for a period of 10 minutes.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 324 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 324 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

other: unhydrous substance

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

other: unhydrous substance

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

Validity criteria: The blank controls (without the test item or reference substance) mean oxygen uptake rate was greater than 20 mg oxygen per one gram of activated sludge (dry weight of suspended solids) in an hour (i.e., 21 mg/g).
The coefficient of variation (RSD) of oxygen uptake rate in control replicates was less than 30% (i.e., ≤ 3%) at the end of main test.

Results with reference substance (positive control):

The EC50 for 3,5-dichlorophenol was 8.86 mg/L which is between the 2 to 25 mg/L of acceptance criteria.

Reported statistics and error estimates:

The respiration rate was calculated from the oxygen consumption of the test solutions as mg O2/L.h (also expressed as mg O2/L. h) between 8 and 2 mg O2/L. The portion of the respiration curve over which the respiration rate was measured was linear. The EC50 calculation (if necessary) probit analysis version 1.5 was used.

Validity criteria fulfilled:

yes

Conclusions:

The EC10 and EC50 of respiration inhibition of activated municipal sewages sludge by the test item barium 4-dodecylphenolate are estimated with > 1,324 mg/L whereas the 3-h NOEC amounts to ≥ 1,324 mg/L (nominal) and ≥ 1,000 mg/L (anhydrous), respectively. No abiotic oxygen consumption measured.

These data can be used for risk assessment purposes and setting a PNEC for sewage treatment plants.

Description of key information

The potential of barium 4 -dodecylphenolate for toxicity to aquatic microorganisms is low since the 3-h NOEC for respiration inhibition of activated sewage sludge (OECD TG 209) is estimated with >= 1,000 mg/L barium 4 -dodecylphenolate (anhydrous).