[No public or meaningful name is available]

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2019

Justification for type of information:

Please refer to read-across justification attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Key result

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

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 1 000 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.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Study period:

1986

Justification for type of information:

Please refer to read-across justification attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Description of key information

Under the conditions of the performed Activated Sludge Respiration Inhibition Test, the EC10 and EC50 values of the source test item were determined as greater than 1000 mg/L. Based on the statistical evaluation in this test the NOEC was 1000 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

No data on the substance itself is available. Therefore, read-across was applied to the source substance Phosphoric acid, 2-ethylhexyl ester, sodium salt (CAS 68186-64-1). This approach is considered appropriate since both substances are UVCB substances consisting of a mono-, bis- and tris- substituted phosphate with C-chains (4 - 6 C), only the cation is different. In the target substance the cation is ammonium, while the source substance has sodium.

Key:

A study according to OECD 209, Regulation (EC) No 440/2008 Method C.11 and OCSPP 850.3300 was performed with the source test item as a preliminary test. The purpose of the 3-hour test was to evaluate the influence of the source item on the activity of the activated sludge by measuring the respiration rate under defined conditions.

The respiration rates (total, heterotrophic and nitrification oxygen uptake rates) of samples of activated sludge fed with synthetic sewage were measured in an enclosed cell containing an oxygen electrode after a contact time of 3 hours. This preliminary test was used to estimate the range of concentrations of the test item needed in a possible definite test for determining the inhibition of oxygen consumption. The test item was investigated in this study at the nominal concentrations of 10, 100 and 1000 mg/L. Defined amounts of the test item were added directly into the test vessels. Triplicate vessels were prepared and investigated at the highest examined test item concentration.

In parallel with the test item treatments, 3,5-Dichlorophenol as positive reference control in a concentrations of 2, 7 and 24.5 mg/L; furthermore, blank (inoculum) control, nitrification controls and abiotic controls were investigated. Abiotic controls (investigated in three parallels) were prepared containing the test item in the concentration of 1000 mg/L, synthetics sewage feed, but no inoculum. In this test no abiotic oxygen consumption was noticed.

All validity criteria of the study were met. The average specific respiration rate of the blank was 31.64 mg O2 / g activated sludge (based on dry weight) in an hour with a coefficient of variation of 4.73 %. The 3-hour EC50 of the reference item 3,5-Dichlorophenol was 16.06 mg/L within the range of 2 mg/L to 25 mg/L, that was required for total respiration (in this study the differentiation between heterotrophic respiration and nitrification was considered as not necessary).

The observed oxygen consumption rates and consequently the specific respiration rates in all examined test item concentrations remained in the range of the blank controls (the average specific respiration rate at 1000 mg/L: 30.30 mg O2/gh). No inhibitory effect of the test item was observed.

Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10 and EC50 values of the source test item are greater than 1000 mg/L. The NOEC was determined to be 1000 mg/L, the highest concentration tested. The specific respiration rates at the examined highest test item concentration of 1000 mg/L were compared with the blank control values using 2-Sample T-test (α=0.05). No statistically significant differences were observed, compared to the blank control values.

In conclusion, this preliminary test demonstrated the absence of inhibition of oxygen consumption by the source substance up to and including the limit concentration of 1000 mg/L, therefore, in line with OECD 209 a definite test is not required.

Supporting:

The toxicity of the source substance to bacteria in sewage sludge was tested in a static system in accordance with Ecological Method No 103. The respiration rate of activated sludge from a domestic wastewater treatment plant was determined in the absence of test substance. Then the corresponding respiration rate of the sludge exposed to nominal test concentrations of 10 and 100 mg/L for 3 hours was determined and compared to the respiration rate of untreated sludge. The microbial activity of the sludge was inhibited at all test concentrations and reduced by 23.5% to 35.3%. The IC50 value for inhibition was higher than 100 mg/L after 3 hours. The sensitivity of the activated sludge was tested and confirmed with the reference substance 3,5 -dichlorophenole.

Based on the structural similarities between the source and the target substance, the target substance is also considered to not be toxic to microorganosms up to 1000 mg/L.